On Mon, Aug 25, 2025 at 05:42:33PM +0200, David Hildenbrand wrote: > On 25.08.25 16:59, Mike Rapoport wrote: > > On Mon, Aug 25, 2025 at 04:38:03PM +0200, David Hildenbrand wrote: > > > On 25.08.25 16:32, Mike Rapoport wrote: > > > > On Mon, Aug 25, 2025 at 02:48:58PM +0200, David Hildenbrand wrote: > > > > > On 23.08.25 10:59, Mike Rapoport wrote: > > > > > > On Fri, Aug 22, 2025 at 08:24:31AM +0200, David Hildenbrand wrote: > > > > > > > On 22.08.25 06:09, Mika Penttilä wrote: > > > > > > > > > > > > > > > > On 8/21/25 23:06, David Hildenbrand wrote: > > > > > > > > > > > > > > > > > All pages were already initialized and set to PageReserved() > > > > > > > > > with a > > > > > > > > > refcount of 1 by MM init code. > > > > > > > > > > > > > > > > Just to be sure, how is this working with MEMBLOCK_RSRV_NOINIT, > > > > > > > > where MM is supposed not to > > > > > > > > initialize struct pages? > > > > > > > > > > > > > > Excellent point, I did not know about that one. > > > > > > > > > > > > > > Spotting that we don't do the same for the head page made me > > > > > > > assume that > > > > > > > it's just a misuse of __init_single_page(). > > > > > > > > > > > > > > But the nasty thing is that we use > > > > > > > memblock_reserved_mark_noinit() to only > > > > > > > mark the tail pages ... > > > > > > > > > > > > And even nastier thing is that when > > > > > > CONFIG_DEFERRED_STRUCT_PAGE_INIT is > > > > > > disabled struct pages are initialized regardless of > > > > > > memblock_reserved_mark_noinit(). > > > > > > > > > > > > I think this patch should go in before your updates: > > > > > > > > > > Shouldn't we fix this in memblock code? > > > > > > > > > > Hacking around that in the memblock_reserved_mark_noinit() user sound > > > > > wrong > > > > > -- and nothing in the doc of memblock_reserved_mark_noinit() spells > > > > > that > > > > > behavior out. > > > > > > > > We can surely update the docs, but unfortunately I don't see how to > > > > avoid > > > > hacking around it in hugetlb. > > > > Since it's used to optimise HVO even further to the point hugetlb open > > > > codes memmap initialization, I think it's fair that it should deal with > > > > all > > > > possible configurations. > > > > > > Remind me, why can't we support memblock_reserved_mark_noinit() when > > > CONFIG_DEFERRED_STRUCT_PAGE_INIT is disabled? > > > > When CONFIG_DEFERRED_STRUCT_PAGE_INIT is disabled we initialize the entire > > memmap early (setup_arch()->free_area_init()), and we may have a bunch of > > memblock_reserved_mark_noinit() afterwards > > Oh, you mean that we get effective memblock modifications after already > initializing the memmap. > > That sounds ... interesting :)
It's memmap, not the free lists. Without deferred init, memblock is active for a while after memmap initialized and before the memory goes to the free lists. > So yeah, we have to document this for memblock_reserved_mark_noinit(). > > Is it also a problem for kexec_handover? With KHO it's also interesting, but it does not support deferred struct page init for now :) > We should do something like: > > diff --git a/mm/memblock.c b/mm/memblock.c > index 154f1d73b61f2..ed4c563d72c32 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -1091,13 +1091,16 @@ int __init_memblock memblock_clear_nomap(phys_addr_t > base, phys_addr_t size) > /** > * memblock_reserved_mark_noinit - Mark a reserved memory region with flag > - * MEMBLOCK_RSRV_NOINIT which results in the struct pages not being > initialized > - * for this region. > + * MEMBLOCK_RSRV_NOINIT which allows for the "struct pages" corresponding > + * to this region not getting initialized, because the caller will take > + * care of it. > * @base: the base phys addr of the region > * @size: the size of the region > * > - * struct pages will not be initialized for reserved memory regions marked > with > - * %MEMBLOCK_RSRV_NOINIT. > + * "struct pages" will not be initialized for reserved memory regions marked > + * with %MEMBLOCK_RSRV_NOINIT if this function is called before > initialization > + * code runs. Without CONFIG_DEFERRED_STRUCT_PAGE_INIT, it is more likely > + * that this function is not effective. > * > * Return: 0 on success, -errno on failure. > */ I have a different version :) diff --git a/include/linux/memblock.h b/include/linux/memblock.h index b96746376e17..d20d091c6343 100644 --- a/include/linux/memblock.h +++ b/include/linux/memblock.h @@ -40,8 +40,9 @@ extern unsigned long long max_possible_pfn; * via a driver, and never indicated in the firmware-provided memory map as * system RAM. This corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED in the * kernel resource tree. - * @MEMBLOCK_RSRV_NOINIT: memory region for which struct pages are - * not initialized (only for reserved regions). + * @MEMBLOCK_RSRV_NOINIT: memory region for which struct pages don't have + * PG_Reserved set and are completely not initialized when + * %CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled (only for reserved regions). * @MEMBLOCK_RSRV_KERN: memory region that is reserved for kernel use, * either explictitly with memblock_reserve_kern() or via memblock * allocation APIs. All memblock allocations set this flag. diff --git a/mm/memblock.c b/mm/memblock.c index 154f1d73b61f..02de5ffb085b 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -1091,13 +1091,15 @@ int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size) /** * memblock_reserved_mark_noinit - Mark a reserved memory region with flag - * MEMBLOCK_RSRV_NOINIT which results in the struct pages not being initialized - * for this region. + * MEMBLOCK_RSRV_NOINIT + * * @base: the base phys addr of the region * @size: the size of the region * - * struct pages will not be initialized for reserved memory regions marked with - * %MEMBLOCK_RSRV_NOINIT. + * The struct pages for the reserved regions marked %MEMBLOCK_RSRV_NOINIT will + * not have %PG_Reserved flag set. + * When %CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, setting this flags also + * completly bypasses the initialization of struct pages for this region. * * Return: 0 on success, -errno on failure. */ > Optimizing the hugetlb code could be done, but I am not sure how high > the priority is (nobody complained so far about the double init). > > -- > Cheers > > David / dhildenb > -- Sincerely yours, Mike.
