Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On Tue, Sep 8, 2020 at 3:46 AM David Hildenbrand wrote: > > On 22.08.20 01:21, Andrew Morton wrote: > > On Wed, 19 Aug 2020 18:53:57 -0700 Dan Williams > > wrote: > > > >>> I think I am missing some important pieces. Bear with me. > >> > >> No worries, also bear with me, I'm going to be offline intermittently > >> until at least mid-September. Hopefully Joao and/or Vishal can jump in > >> on this discussion. > > > > Ordinarily I'd prefer a refresh for 2+ week-old series such as > > this. > > > > But given that v4 all applies OK and that Dan has pending outages, I'll > > scoop up this version, even though at least one change has been suggested. > > > > Should I try to fix patch #11 while Dan is away? Because I think at > least two things in there are wrong (and it would have been better to > split that patch into reviewable pieces). Hey David, Back now, I'll take a look. I didn't immediately see a way to meaningfully break up that patch without some dead-code steps in the conversion, but I'll take another run at it.
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On 22.08.20 01:21, Andrew Morton wrote: > On Wed, 19 Aug 2020 18:53:57 -0700 Dan Williams > wrote: > >>> I think I am missing some important pieces. Bear with me. >> >> No worries, also bear with me, I'm going to be offline intermittently >> until at least mid-September. Hopefully Joao and/or Vishal can jump in >> on this discussion. > > Ordinarily I'd prefer a refresh for 2+ week-old series such as > this. > > But given that v4 all applies OK and that Dan has pending outages, I'll > scoop up this version, even though at least one change has been suggested. > Should I try to fix patch #11 while Dan is away? Because I think at least two things in there are wrong (and it would have been better to split that patch into reviewable pieces). -- Thanks, David / dhildenb
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On 8/22/2020 7:21 AM, Andrew Morton wrote: > On Wed, 19 Aug 2020 18:53:57 -0700 Dan Williams > wrote: > >>> I think I am missing some important pieces. Bear with me. >> >> No worries, also bear with me, I'm going to be offline intermittently >> until at least mid-September. Hopefully Joao and/or Vishal can jump in >> on this discussion. > > Ordinarily I'd prefer a refresh for 2+ week-old series such as > this. > > But given that v4 all applies OK and that Dan has pending outages, I'll > scoop up this version, even though at least one change has been suggested. > > Also, this series has killed Zhen Lei's little cleanup > (http://lkml.kernel.org/r/20200817065926.2239-1-thunder.leiz...@huawei.com). > I don't think the affected code was moved elsewhere, so I'll drop that > patch. OK, this patch is really optional. > > > . >
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On Wed, 19 Aug 2020 18:53:57 -0700 Dan Williams wrote: > > I think I am missing some important pieces. Bear with me. > > No worries, also bear with me, I'm going to be offline intermittently > until at least mid-September. Hopefully Joao and/or Vishal can jump in > on this discussion. Ordinarily I'd prefer a refresh for 2+ week-old series such as this. But given that v4 all applies OK and that Dan has pending outages, I'll scoop up this version, even though at least one change has been suggested. Also, this series has killed Zhen Lei's little cleanup (http://lkml.kernel.org/r/20200817065926.2239-1-thunder.leiz...@huawei.com). I don't think the affected code was moved elsewhere, so I'll drop that patch.
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
> Am 21.08.2020 um 23:34 schrieb David Hildenbrand : > > > >>> Am 21.08.2020 um 23:17 schrieb Dan Williams : >>> >>> On Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand >>> wrote: >>> On 21.08.20 20:27, Dan Williams wrote: On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wrote: > >>> >>> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not >>> automatically used in the buddy during boot, but remains untouched >>> (similar to pmem). But as it involves ACPI as well, it could also be >>> used on arm64 (-e820), correct? >> >> Correct, arm64 also gets the EFI support for enumerating memory this >> way. However, I would clarify that whether soft-reserved is given to >> the buddy allocator by default or not is the kernel's policy choice, >> "buddy-by-default" is ok and is what will happen anyways with older >> kernels on platforms that enumerate a memory range this way. > > Is "soft-reserved" then the right terminology for that? It sounds very > x86-64/e820 specific. Maybe a compressed for of "performance > differentiated memory" might be a better fit to expose to user space, no? No. The EFI "Specific Purpose" bit is an attribute independent of e820, it's x86-Linux that entangles those together. There is no requirement for platform firmware to use that designation even for drastic performance differentiation between ranges, and conversely there is no requirement that memory *with* that designation has any performance difference compared to the default memory pool. So it really is a reservation policy about a memory range to keep out of the buddy allocator by default. >>> >>> Okay, still "soft-reserved" is x86-64 specific, no? >> >> There's nothing preventing other EFI archs, or a similar designation >> in another firmware spec, picking up this policy. >> >>> (AFAIK, >>> "soft-reserved" will be visible in /proc/iomem, or am I confusing >>> stuff?) >> >> No, you're correct. >> >>> IOW, it "performance differentiated" is not universally >>> applicable, maybe "specific purpose memory" is ? >> >> Those bikeshed colors don't seem an improvement to me. >> >> "Soft-reserved" actually tells you something about the kernel policy >> for the memory. The criticism of "specific purpose" that led to >> calling it "soft-reserved" in Linux is the fact that "specific" is >> undefined as far as the firmware knows, and "specific" may have >> different applications based on the platform user. "Soft-reserved" >> like "Reserved" tells you that a driver policy might be in play for >> that memory. >> >> Also note that the current color of the bikeshed has already shipped since >> v5.5: >> >> 262b45ae3ab4 x86/efi: EFI soft reservation to E820 enumeration >> > > I was asking because I was struggling to even understand what „soft-reserved“ > is and I could bet most people have no clue what that is supposed to be. > > In contrast „persistent memory“ or „special purpose memory“ in /proc/iomem is > something normal (Linux using) human beings can understand. Obviously s/normal/most/ Cheers!
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
> Am 21.08.2020 um 23:34 schrieb David Hildenbrand : > > > >>> Am 21.08.2020 um 23:17 schrieb Dan Williams : >>> >>> On Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand >>> wrote: >>> On 21.08.20 20:27, Dan Williams wrote: On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wrote: > >>> >>> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not >>> automatically used in the buddy during boot, but remains untouched >>> (similar to pmem). But as it involves ACPI as well, it could also be >>> used on arm64 (-e820), correct? >> >> Correct, arm64 also gets the EFI support for enumerating memory this >> way. However, I would clarify that whether soft-reserved is given to >> the buddy allocator by default or not is the kernel's policy choice, >> "buddy-by-default" is ok and is what will happen anyways with older >> kernels on platforms that enumerate a memory range this way. > > Is "soft-reserved" then the right terminology for that? It sounds very > x86-64/e820 specific. Maybe a compressed for of "performance > differentiated memory" might be a better fit to expose to user space, no? No. The EFI "Specific Purpose" bit is an attribute independent of e820, it's x86-Linux that entangles those together. There is no requirement for platform firmware to use that designation even for drastic performance differentiation between ranges, and conversely there is no requirement that memory *with* that designation has any performance difference compared to the default memory pool. So it really is a reservation policy about a memory range to keep out of the buddy allocator by default. >>> >>> Okay, still "soft-reserved" is x86-64 specific, no? >> >> There's nothing preventing other EFI archs, or a similar designation >> in another firmware spec, picking up this policy. >> >>> (AFAIK, >>> "soft-reserved" will be visible in /proc/iomem, or am I confusing >>> stuff?) >> >> No, you're correct. >> >>> IOW, it "performance differentiated" is not universally >>> applicable, maybe "specific purpose memory" is ? >> >> Those bikeshed colors don't seem an improvement to me. >> >> "Soft-reserved" actually tells you something about the kernel policy >> for the memory. The criticism of "specific purpose" that led to >> calling it "soft-reserved" in Linux is the fact that "specific" is >> undefined as far as the firmware knows, and "specific" may have >> different applications based on the platform user. "Soft-reserved" >> like "Reserved" tells you that a driver policy might be in play for >> that memory. >> >> Also note that the current color of the bikeshed has already shipped since >> v5.5: >> >> 262b45ae3ab4 x86/efi: EFI soft reservation to E820 enumeration >> > > I was asking because I was struggling to even understand what „soft-reserved“ > is and I could bet most people have no clue what that is supposed to be. > > In contrast „persistent memory“ or „special purpose memory“ in /proc/iomem is > something normal (Linux using) human beings can understand. s/normal/most/ of course :)
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On 21.08.20 23:33, David Hildenbrand wrote: > > >> Am 21.08.2020 um 23:17 schrieb Dan Williams : >> >> On Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand wrote: >>> On 21.08.20 20:27, Dan Williams wrote: On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wrote: > >>> >>> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not >>> automatically used in the buddy during boot, but remains untouched >>> (similar to pmem). But as it involves ACPI as well, it could also be >>> used on arm64 (-e820), correct? >> >> Correct, arm64 also gets the EFI support for enumerating memory this >> way. However, I would clarify that whether soft-reserved is given to >> the buddy allocator by default or not is the kernel's policy choice, >> "buddy-by-default" is ok and is what will happen anyways with older >> kernels on platforms that enumerate a memory range this way. > > Is "soft-reserved" then the right terminology for that? It sounds very > x86-64/e820 specific. Maybe a compressed for of "performance > differentiated memory" might be a better fit to expose to user space, no? No. The EFI "Specific Purpose" bit is an attribute independent of e820, it's x86-Linux that entangles those together. There is no requirement for platform firmware to use that designation even for drastic performance differentiation between ranges, and conversely there is no requirement that memory *with* that designation has any performance difference compared to the default memory pool. So it really is a reservation policy about a memory range to keep out of the buddy allocator by default. >>> >>> Okay, still "soft-reserved" is x86-64 specific, no? >> >> There's nothing preventing other EFI archs, or a similar designation >> in another firmware spec, picking up this policy. >> >>> (AFAIK, >>> "soft-reserved" will be visible in /proc/iomem, or am I confusing >>> stuff?) >> >> No, you're correct. >> >>> IOW, it "performance differentiated" is not universally >>> applicable, maybe "specific purpose memory" is ? >> >> Those bikeshed colors don't seem an improvement to me. >> >> "Soft-reserved" actually tells you something about the kernel policy >> for the memory. The criticism of "specific purpose" that led to >> calling it "soft-reserved" in Linux is the fact that "specific" is >> undefined as far as the firmware knows, and "specific" may have >> different applications based on the platform user. "Soft-reserved" >> like "Reserved" tells you that a driver policy might be in play for >> that memory. >> >> Also note that the current color of the bikeshed has already shipped since >> v5.5: >> >> 262b45ae3ab4 x86/efi: EFI soft reservation to E820 enumeration >> > > I was asking because I was struggling to even understand what „soft-reserved“ > is and I could bet most people have no clue what that is supposed to be. > > In contrast „persistent memory“ or „special purpose memory“ in /proc/iomem is > something normal (Linux using) human beings can understand. s/normal/most/ , shouldn't be writing emails from my smartphone. Cheers! -- Thanks, David / dhildenb
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
> Am 21.08.2020 um 23:17 schrieb Dan Williams : > > On Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand wrote: >> >>> On 21.08.20 20:27, Dan Williams wrote: >>> On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wrote: >> >> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not >> automatically used in the buddy during boot, but remains untouched >> (similar to pmem). But as it involves ACPI as well, it could also be >> used on arm64 (-e820), correct? > > Correct, arm64 also gets the EFI support for enumerating memory this > way. However, I would clarify that whether soft-reserved is given to > the buddy allocator by default or not is the kernel's policy choice, > "buddy-by-default" is ok and is what will happen anyways with older > kernels on platforms that enumerate a memory range this way. Is "soft-reserved" then the right terminology for that? It sounds very x86-64/e820 specific. Maybe a compressed for of "performance differentiated memory" might be a better fit to expose to user space, no? >>> >>> No. The EFI "Specific Purpose" bit is an attribute independent of >>> e820, it's x86-Linux that entangles those together. There is no >>> requirement for platform firmware to use that designation even for >>> drastic performance differentiation between ranges, and conversely >>> there is no requirement that memory *with* that designation has any >>> performance difference compared to the default memory pool. So it >>> really is a reservation policy about a memory range to keep out of the >>> buddy allocator by default. >> >> Okay, still "soft-reserved" is x86-64 specific, no? > > There's nothing preventing other EFI archs, or a similar designation > in another firmware spec, picking up this policy. > >> (AFAIK, >> "soft-reserved" will be visible in /proc/iomem, or am I confusing >> stuff?) > > No, you're correct. > >> IOW, it "performance differentiated" is not universally >> applicable, maybe "specific purpose memory" is ? > > Those bikeshed colors don't seem an improvement to me. > > "Soft-reserved" actually tells you something about the kernel policy > for the memory. The criticism of "specific purpose" that led to > calling it "soft-reserved" in Linux is the fact that "specific" is > undefined as far as the firmware knows, and "specific" may have > different applications based on the platform user. "Soft-reserved" > like "Reserved" tells you that a driver policy might be in play for > that memory. > > Also note that the current color of the bikeshed has already shipped since > v5.5: > > 262b45ae3ab4 x86/efi: EFI soft reservation to E820 enumeration > I was asking because I was struggling to even understand what „soft-reserved“ is and I could bet most people have no clue what that is supposed to be. In contrast „persistent memory“ or „special purpose memory“ in /proc/iomem is something normal (Linux using) human beings can understand. But anyhow, just details, and you‘re telling me that that ship already sailed. So no further comments from my side. Thanks for all the info!
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand wrote: > > On 21.08.20 20:27, Dan Williams wrote: > > On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wrote: > >> > > 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not > automatically used in the buddy during boot, but remains untouched > (similar to pmem). But as it involves ACPI as well, it could also be > used on arm64 (-e820), correct? > >>> > >>> Correct, arm64 also gets the EFI support for enumerating memory this > >>> way. However, I would clarify that whether soft-reserved is given to > >>> the buddy allocator by default or not is the kernel's policy choice, > >>> "buddy-by-default" is ok and is what will happen anyways with older > >>> kernels on platforms that enumerate a memory range this way. > >> > >> Is "soft-reserved" then the right terminology for that? It sounds very > >> x86-64/e820 specific. Maybe a compressed for of "performance > >> differentiated memory" might be a better fit to expose to user space, no? > > > > No. The EFI "Specific Purpose" bit is an attribute independent of > > e820, it's x86-Linux that entangles those together. There is no > > requirement for platform firmware to use that designation even for > > drastic performance differentiation between ranges, and conversely > > there is no requirement that memory *with* that designation has any > > performance difference compared to the default memory pool. So it > > really is a reservation policy about a memory range to keep out of the > > buddy allocator by default. > > Okay, still "soft-reserved" is x86-64 specific, no? There's nothing preventing other EFI archs, or a similar designation in another firmware spec, picking up this policy. > (AFAIK, > "soft-reserved" will be visible in /proc/iomem, or am I confusing > stuff?) No, you're correct. > IOW, it "performance differentiated" is not universally > applicable, maybe "specific purpose memory" is ? Those bikeshed colors don't seem an improvement to me. "Soft-reserved" actually tells you something about the kernel policy for the memory. The criticism of "specific purpose" that led to calling it "soft-reserved" in Linux is the fact that "specific" is undefined as far as the firmware knows, and "specific" may have different applications based on the platform user. "Soft-reserved" like "Reserved" tells you that a driver policy might be in play for that memory. Also note that the current color of the bikeshed has already shipped since v5.5: 262b45ae3ab4 x86/efi: EFI soft reservation to E820 enumeration
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wrote: > > >> > >> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not > >> automatically used in the buddy during boot, but remains untouched > >> (similar to pmem). But as it involves ACPI as well, it could also be > >> used on arm64 (-e820), correct? > > > > Correct, arm64 also gets the EFI support for enumerating memory this > > way. However, I would clarify that whether soft-reserved is given to > > the buddy allocator by default or not is the kernel's policy choice, > > "buddy-by-default" is ok and is what will happen anyways with older > > kernels on platforms that enumerate a memory range this way. > > Is "soft-reserved" then the right terminology for that? It sounds very > x86-64/e820 specific. Maybe a compressed for of "performance > differentiated memory" might be a better fit to expose to user space, no? No. The EFI "Specific Purpose" bit is an attribute independent of e820, it's x86-Linux that entangles those together. There is no requirement for platform firmware to use that designation even for drastic performance differentiation between ranges, and conversely there is no requirement that memory *with* that designation has any performance difference compared to the default memory pool. So it really is a reservation policy about a memory range to keep out of the buddy allocator by default. [..] > > Both, but note that PMEM is already hard-reserved by default. > > Soft-reserved is about a memory range that, for example, an > > administrator may want to reserve 100% for a weather simulation where > > if even a small amount of memory was stolen for the page cache the > > application may not meet its performance targets. It could also be a > > memory range that is so slow that only applications with higher > > latency tolerances would be prepared to consume it. > > > > In other words the soft-reserved memory can be used to indicate memory > > that is either too precious, or too slow for general purpose OS > > allocations. > > Right, so actually performance-differentiated in any way :) ... or not differentiated at all which is Joao's use case for example. [..] > > Numa node numbers / are how performance differentiated memory ranges > > are enumerated. The expectation is that all distinct performance > > memory targets have unique ACPI proximity domains and Linux numa node > > numbers as a result. > > Makes sense to me (although it's somehow weird, because memory of the > same socket/node would be represented via different NUMA nodes), thanks! Yes, numa ids as only physical socket identifiers is no longer a reliable assumption since the introduction of the ACPI HMAT.
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On 21.08.20 20:27, Dan Williams wrote: > On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wrote: >> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not automatically used in the buddy during boot, but remains untouched (similar to pmem). But as it involves ACPI as well, it could also be used on arm64 (-e820), correct? >>> >>> Correct, arm64 also gets the EFI support for enumerating memory this >>> way. However, I would clarify that whether soft-reserved is given to >>> the buddy allocator by default or not is the kernel's policy choice, >>> "buddy-by-default" is ok and is what will happen anyways with older >>> kernels on platforms that enumerate a memory range this way. >> >> Is "soft-reserved" then the right terminology for that? It sounds very >> x86-64/e820 specific. Maybe a compressed for of "performance >> differentiated memory" might be a better fit to expose to user space, no? > > No. The EFI "Specific Purpose" bit is an attribute independent of > e820, it's x86-Linux that entangles those together. There is no > requirement for platform firmware to use that designation even for > drastic performance differentiation between ranges, and conversely > there is no requirement that memory *with* that designation has any > performance difference compared to the default memory pool. So it > really is a reservation policy about a memory range to keep out of the > buddy allocator by default. Okay, still "soft-reserved" is x86-64 specific, no? (AFAIK, "soft-reserved" will be visible in /proc/iomem, or am I confusing stuff?) IOW, it "performance differentiated" is not universally applicable, maybe "specific purpose memory" is ? -- Thanks, David / dhildenb
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
>>
>> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not
>> automatically used in the buddy during boot, but remains untouched
>> (similar to pmem). But as it involves ACPI as well, it could also be
>> used on arm64 (-e820), correct?
>
> Correct, arm64 also gets the EFI support for enumerating memory this
> way. However, I would clarify that whether soft-reserved is given to
> the buddy allocator by default or not is the kernel's policy choice,
> "buddy-by-default" is ok and is what will happen anyways with older
> kernels on platforms that enumerate a memory range this way.
Is "soft-reserved" then the right terminology for that? It sounds very
x86-64/e820 specific. Maybe a compressed for of "performance
differentiated memory" might be a better fit to expose to user space, no?
>
>> 2. Soft-reserved memory is volatile RAM with differing performance
>> characteristics ("performance differentiated memory"). What would be
>> examples of such memory?
>
> Likely the most prominent one that drove the creation of the "EFI
> Specific Purpose" attribute bit is high-bandwidth memory. One concrete
> example of that was a platform called Knights Landing [1] that ended
> up shipping firmware that lied to the OS about the latency
> characteristics of the memory to try to reverse engineer OS behavior
> to not allocate from that memory range by default. With the EFI
> attribute firmware performance tables can tell the truth about the
> performance characteristics of the memory range *and* indicate that
> the OS not use it for general purpose allocations by default.
Thanks for clarifying!
>
> [1]:
> https://software.intel.com/content/www/us/en/develop/blogs/an-intro-to-mcdram-high-bandwidth-memory-on-knights-landing.html
>
>> Like, memory that is faster than RAM (scratch
>> pad), or slower (pmem)? Or both? :)
>
> Both, but note that PMEM is already hard-reserved by default.
> Soft-reserved is about a memory range that, for example, an
> administrator may want to reserve 100% for a weather simulation where
> if even a small amount of memory was stolen for the page cache the
> application may not meet its performance targets. It could also be a
> memory range that is so slow that only applications with higher
> latency tolerances would be prepared to consume it.
>
> In other words the soft-reserved memory can be used to indicate memory
> that is either too precious, or too slow for general purpose OS
> allocations.
Right, so actually performance-differentiated in any way :)
>
>> Is it a valid use case to use pmem
>> in a hypervisor to back this memory?
>
> Depends on the pmem. That performance capability is indicated by the
> ACPI HMAT, not the EFI soft-reserved designation.
>
>> 3. There seem to be use cases where "soft-reserved" memory is used via
>> DAX. What is an example use case? I assume it's *not* to treat it like
>> PMEM but instead e.g., use it as a fast buffer inside applications or
>> similar.
>
> Right, in that weather-simulation example that application could just
> mmap /dev/daxX.Y and never worry about contending for the "fast
> memory" resource on the platform. Alternatively if that resource needs
> to be shared and/or over-commited then kernel memory-management
> services are needed and that dax-device can be assigned to kmem.
>
>> 4. There seem to be use cases where some part of "soft-reserved" memory
>> is used via DAX, some other is given to the buddy. What is an example
>> use case? Is this really necessary or only some theoretical use case?
>
> It's as necessary as pmem namespace partitioning, or the inclusion of
> dax-kmem upstream in the first place. In that kmem case the motivation
> was that some users want a portion of pmem provisioned for storage and
> some for volatile usage. The motivation is similar here, platform
> firmware can only identify memory attributes on coarse boundaries,
> finer grained provisioning decisions are up to the administrator /
> platform-owner and the kernel is a just a facilitator of that policy.
>
>>
>> 5. The "provisioned along performance relevant address boundaries." part
>> is unclear to me. Can you give an example of how this would look like
>> from user space? Like, split that memory in blocks of size X with
>> alignment Y and give them to separate applications?
>
> One example of platform address boundaries are the memory address
> ranges that alias in a direct-mapped memory-side-cache. In the
> direct-map-cache aliasing may repeat every N GBs where N is the ratio
> of far-to-near memory. ("Near memory" == cache "Far memory" ==
> backing memory). Also refer back to the background in the page
> allocator shuffling patches [2]. With this partitioning mechanism you
> could, for one example use case, assign different VMs to exclusive
> colors in the memory side cache.
Interesting, thanks!
>
> [2]:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e900a918b098
>
>> 6. If you add such
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
On Mon, Aug 3, 2020 at 12:48 AM David Hildenbrand wrote:
>
> [...]
>
> > Well, no v5.8-rc8 to line this up for v5.9, so next best is early
> > integration into -mm before other collisions develop.
> >
> > Chatted with Justin offline and it currently appears that the missing
> > numa information is the fault of the platform firmware to populate all
> > the necessary NUMA data in the NFIT.
>
> I'm planning on looking at some bits of this series this week, but some
> questions upfront ...
>
> >
> > ---
> > Cover:
> >
> > The device-dax facility allows an address range to be directly mapped
> > through a chardev, or optionally hotplugged to the core kernel page
> > allocator as System-RAM. It is the mechanism for converting persistent
> > memory (pmem) to be used as another volatile memory pool i.e. the
> > current Memory Tiering hot topic on linux-mm.
> >
> > In the case of pmem the nvdimm-namespace-label mechanism can sub-divide
> > it, but that labeling mechanism is not available / applicable to
> > soft-reserved ("EFI specific purpose") memory [3]. This series provides
> > a sysfs-mechanism for the daxctl utility to enable provisioning of
> > volatile-soft-reserved memory ranges.
> >
> > The motivations for this facility are:
> >
> > 1/ Allow performance differentiated memory ranges to be split between
> >kernel-managed and directly-accessed use cases.
> >
> > 2/ Allow physical memory to be provisioned along performance relevant
> >address boundaries. For example, divide a memory-side cache [4] along
> >cache-color boundaries.
> >
> > 3/ Parcel out soft-reserved memory to VMs using device-dax as a security
> >/ permissions boundary [5]. Specifically I have seen people (ab)using
> >memmap=nn!ss (mark System-RAM as Persistent Memory) just to get the
> >device-dax interface on custom address ranges. A follow-on for the VM
> >use case is to teach device-dax to dynamically allocate 'struct page' at
> >runtime to reduce the duplication of 'struct page' space in both the
> >guest and the host kernel for the same physical pages.
>
>
> I think I am missing some important pieces. Bear with me.
No worries, also bear with me, I'm going to be offline intermittently
until at least mid-September. Hopefully Joao and/or Vishal can jump in
on this discussion.
>
> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not
> automatically used in the buddy during boot, but remains untouched
> (similar to pmem). But as it involves ACPI as well, it could also be
> used on arm64 (-e820), correct?
Correct, arm64 also gets the EFI support for enumerating memory this
way. However, I would clarify that whether soft-reserved is given to
the buddy allocator by default or not is the kernel's policy choice,
"buddy-by-default" is ok and is what will happen anyways with older
kernels on platforms that enumerate a memory range this way.
> 2. Soft-reserved memory is volatile RAM with differing performance
> characteristics ("performance differentiated memory"). What would be
> examples of such memory?
Likely the most prominent one that drove the creation of the "EFI
Specific Purpose" attribute bit is high-bandwidth memory. One concrete
example of that was a platform called Knights Landing [1] that ended
up shipping firmware that lied to the OS about the latency
characteristics of the memory to try to reverse engineer OS behavior
to not allocate from that memory range by default. With the EFI
attribute firmware performance tables can tell the truth about the
performance characteristics of the memory range *and* indicate that
the OS not use it for general purpose allocations by default.
[1]:
https://software.intel.com/content/www/us/en/develop/blogs/an-intro-to-mcdram-high-bandwidth-memory-on-knights-landing.html
> Like, memory that is faster than RAM (scratch
> pad), or slower (pmem)? Or both? :)
Both, but note that PMEM is already hard-reserved by default.
Soft-reserved is about a memory range that, for example, an
administrator may want to reserve 100% for a weather simulation where
if even a small amount of memory was stolen for the page cache the
application may not meet its performance targets. It could also be a
memory range that is so slow that only applications with higher
latency tolerances would be prepared to consume it.
In other words the soft-reserved memory can be used to indicate memory
that is either too precious, or too slow for general purpose OS
allocations.
> Is it a valid use case to use pmem
> in a hypervisor to back this memory?
Depends on the pmem. That performance capability is indicated by the
ACPI HMAT, not the EFI soft-reserved designation.
> 3. There seem to be use cases where "soft-reserved" memory is used via
> DAX. What is an example use case? I assume it's *not* to treat it like
> PMEM but instead e.g., use it as a fast buffer inside applications or
> similar.
Right, in that weather-simulation example that application could just
mmap /dev/daxX.Y
Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
[...]
> Well, no v5.8-rc8 to line this up for v5.9, so next best is early
> integration into -mm before other collisions develop.
>
> Chatted with Justin offline and it currently appears that the missing
> numa information is the fault of the platform firmware to populate all
> the necessary NUMA data in the NFIT.
I'm planning on looking at some bits of this series this week, but some
questions upfront ...
>
> ---
> Cover:
>
> The device-dax facility allows an address range to be directly mapped
> through a chardev, or optionally hotplugged to the core kernel page
> allocator as System-RAM. It is the mechanism for converting persistent
> memory (pmem) to be used as another volatile memory pool i.e. the
> current Memory Tiering hot topic on linux-mm.
>
> In the case of pmem the nvdimm-namespace-label mechanism can sub-divide
> it, but that labeling mechanism is not available / applicable to
> soft-reserved ("EFI specific purpose") memory [3]. This series provides
> a sysfs-mechanism for the daxctl utility to enable provisioning of
> volatile-soft-reserved memory ranges.
>
> The motivations for this facility are:
>
> 1/ Allow performance differentiated memory ranges to be split between
>kernel-managed and directly-accessed use cases.
>
> 2/ Allow physical memory to be provisioned along performance relevant
>address boundaries. For example, divide a memory-side cache [4] along
>cache-color boundaries.
>
> 3/ Parcel out soft-reserved memory to VMs using device-dax as a security
>/ permissions boundary [5]. Specifically I have seen people (ab)using
>memmap=nn!ss (mark System-RAM as Persistent Memory) just to get the
>device-dax interface on custom address ranges. A follow-on for the VM
>use case is to teach device-dax to dynamically allocate 'struct page' at
>runtime to reduce the duplication of 'struct page' space in both the
>guest and the host kernel for the same physical pages.
I think I am missing some important pieces. Bear with me.
1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not
automatically used in the buddy during boot, but remains untouched
(similar to pmem). But as it involves ACPI as well, it could also be
used on arm64 (-e820), correct?
2. Soft-reserved memory is volatile RAM with differing performance
characteristics ("performance differentiated memory"). What would be
examples of such memory? Like, memory that is faster than RAM (scratch
pad), or slower (pmem)? Or both? :) Is it a valid use case to use pmem
in a hypervisor to back this memory?
3. There seem to be use cases where "soft-reserved" memory is used via
DAX. What is an example use case? I assume it's *not* to treat it like
PMEM but instead e.g., use it as a fast buffer inside applications or
similar.
4. There seem to be use cases where some part of "soft-reserved" memory
is used via DAX, some other is given to the buddy. What is an example
use case? Is this really necessary or only some theoretical use case?
5. The "provisioned along performance relevant address boundaries." part
is unclear to me. Can you give an example of how this would look like
from user space? Like, split that memory in blocks of size X with
alignment Y and give them to separate applications?
6. If you add such memory to the buddy, is there any way the system can
differentiate it from other memory? E.g., via fake/other NUMA nodes?
Also, can you give examples of how kmem-added memory is represented in
/proc/iomem for a) pmem and b) soft-resered memory after this series
(skimming over the patches, I think there is a change for pmem, right?)?
I am really wondering if it's the right approach to squeeze this into
our pmem/nvdimm infrastructure just because it's easy to do. E.g., man
"ndctl" - "ndctl - Manage "libnvdimm" subsystem devices (Non-volatile
Memory)" speaks explicitly about non-volatile memory.
>
> [2]:
> http://lore.kernel.org/r/20200713160837.13774-11-joao.m.mart...@oracle.com
> [3]:
> http://lore.kernel.org/r/157309097008.1579826.12818463304589384434.st...@dwillia2-desk3.amr.corp.intel.com
> [4]:
> http://lore.kernel.org/r/154899811738.3165233.12325692939590944259.st...@dwillia2-desk3.amr.corp.intel.com
> [5]: http://lore.kernel.org/r/20200110190313.17144-1-joao.m.mart...@oracle.com
>
> ---
>
> Dan Williams (19):
> x86/numa: Cleanup configuration dependent command-line options
> x86/numa: Add 'nohmat' option
> efi/fake_mem: Arrange for a resource entry per efi_fake_mem instance
> ACPI: HMAT: Refactor hmat_register_target_device to hmem_register_device
> resource: Report parent to walk_iomem_res_desc() callback
> mm/memory_hotplug: Introduce default phys_to_target_node()
> implementation
> ACPI: HMAT: Attach a device for each soft-reserved range
> device-dax: Drop the dax_region.pfn_flags attribute
> device-dax: Move instance creation parameters to 'struct dev_dax_data'
> device-dax: Make pgmap optional for
[PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges
Changes since v3 [1]:
- Update x86 boot options documentation for 'nohmat' (Randy)
- Fixup a handful of kbuild robot reports, the most significant being
moving usage of PUD_SIZE and PMD_SIZE under
#ifdef CONFIG_TRANSPARENT_HUGEPAGE protection.
[1]:
http://lore.kernel.org/r/159625229779.3040297.11363509688097221416.st...@dwillia2-desk3.amr.corp.intel.com
---
Merge notes:
Well, no v5.8-rc8 to line this up for v5.9, so next best is early
integration into -mm before other collisions develop.
Chatted with Justin offline and it currently appears that the missing
numa information is the fault of the platform firmware to populate all
the necessary NUMA data in the NFIT.
---
Cover:
The device-dax facility allows an address range to be directly mapped
through a chardev, or optionally hotplugged to the core kernel page
allocator as System-RAM. It is the mechanism for converting persistent
memory (pmem) to be used as another volatile memory pool i.e. the
current Memory Tiering hot topic on linux-mm.
In the case of pmem the nvdimm-namespace-label mechanism can sub-divide
it, but that labeling mechanism is not available / applicable to
soft-reserved ("EFI specific purpose") memory [3]. This series provides
a sysfs-mechanism for the daxctl utility to enable provisioning of
volatile-soft-reserved memory ranges.
The motivations for this facility are:
1/ Allow performance differentiated memory ranges to be split between
kernel-managed and directly-accessed use cases.
2/ Allow physical memory to be provisioned along performance relevant
address boundaries. For example, divide a memory-side cache [4] along
cache-color boundaries.
3/ Parcel out soft-reserved memory to VMs using device-dax as a security
/ permissions boundary [5]. Specifically I have seen people (ab)using
memmap=nn!ss (mark System-RAM as Persistent Memory) just to get the
device-dax interface on custom address ranges. A follow-on for the VM
use case is to teach device-dax to dynamically allocate 'struct page' at
runtime to reduce the duplication of 'struct page' space in both the
guest and the host kernel for the same physical pages.
[2]: http://lore.kernel.org/r/20200713160837.13774-11-joao.m.mart...@oracle.com
[3]:
http://lore.kernel.org/r/157309097008.1579826.12818463304589384434.st...@dwillia2-desk3.amr.corp.intel.com
[4]:
http://lore.kernel.org/r/154899811738.3165233.12325692939590944259.st...@dwillia2-desk3.amr.corp.intel.com
[5]: http://lore.kernel.org/r/20200110190313.17144-1-joao.m.mart...@oracle.com
---
Dan Williams (19):
x86/numa: Cleanup configuration dependent command-line options
x86/numa: Add 'nohmat' option
efi/fake_mem: Arrange for a resource entry per efi_fake_mem instance
ACPI: HMAT: Refactor hmat_register_target_device to hmem_register_device
resource: Report parent to walk_iomem_res_desc() callback
mm/memory_hotplug: Introduce default phys_to_target_node() implementation
ACPI: HMAT: Attach a device for each soft-reserved range
device-dax: Drop the dax_region.pfn_flags attribute
device-dax: Move instance creation parameters to 'struct dev_dax_data'
device-dax: Make pgmap optional for instance creation
device-dax: Kill dax_kmem_res
device-dax: Add an allocation interface for device-dax instances
device-dax: Introduce 'seed' devices
drivers/base: Make device_find_child_by_name() compatible with sysfs
inputs
device-dax: Add resize support
mm/memremap_pages: Convert to 'struct range'
mm/memremap_pages: Support multiple ranges per invocation
device-dax: Add dis-contiguous resource support
device-dax: Introduce 'mapping' devices
Joao Martins (4):
device-dax: Make align a per-device property
device-dax: Add an 'align' attribute
dax/hmem: Introduce dax_hmem.region_idle parameter
device-dax: Add a range mapping allocation attribute
Documentation/x86/x86_64/boot-options.rst |4
arch/powerpc/kvm/book3s_hv_uvmem.c| 14
arch/x86/include/asm/numa.h |8
arch/x86/kernel/e820.c| 16
arch/x86/mm/numa.c| 11
arch/x86/mm/numa_emulation.c |3
arch/x86/xen/enlighten_pv.c |2
drivers/acpi/numa/hmat.c | 76 --
drivers/acpi/numa/srat.c |9
drivers/base/core.c |2
drivers/dax/Kconfig |4
drivers/dax/Makefile |3
drivers/dax/bus.c | 1046 +++--
drivers/dax/bus.h | 28 -
drivers/dax/dax-private.h | 60 +-
drivers/dax/device.c | 134 ++--
drivers/dax/hmem.c| 56 --
drivers/dax/hmem/Makefile |6
drivers/dax/hmem/device.c | 100 +++
drivers/dax/hmem/hmem.c
