Re: [PATCH v3 1/6] mm/thp: add prep_transhuge_device_private_page()
On 11/5/20 11:55 PM, Christoph Hellwig wrote:
On Thu, Nov 05, 2020 at 04:51:42PM -0800, Ralph Campbell wrote:
+extern void prep_transhuge_device_private_page(struct page *page);
No need for the extern.
Right, I was just copying the style.
Would you like to see a preparatory patch that removes extern for the other
declarations in huge_mm.h?
+static inline void prep_transhuge_device_private_page(struct page *page)
+{
+}
Is the code to call this even reachable if THP support is configured
out? If not just declaring it unconditionally and letting dead code
elimination do its job might be a tad cleaner.
The HMM test driver depends on TRANSPARENT_HUGEPAGE but the nouveau SVM
option doesn't and SVM is still useful if TRANSPARENT_HUGEPAGE is not
configured.
The problem with defining prep_transhuge_device_private_page() in huge_mm.h
as a static inline function is that prep_compound_page() and
prep_transhuge_page()
would have to be EXPORT_SYMBOL_GPL which are currently mm internal only.
The intent is to make this helper callable by separate device driver modules
using struct pages created with memremap_pages().
+void prep_transhuge_device_private_page(struct page *page)
I think a kerneldoc comment explaining what this function is useful for
would be helpful.
That is a good idea. I'll add it to v4.
Re: [PATCH v3 1/6] mm/thp: add prep_transhuge_device_private_page()
On 11/6/20 4:14 AM, Matthew Wilcox wrote:
On Thu, Nov 05, 2020 at 04:51:42PM -0800, Ralph Campbell wrote:
Add a helper function to allow device drivers to create device private
transparent huge pages. This is intended to help support device private
THP migrations.
I think you'd be better off with these calling conventions:
-void prep_transhuge_page(struct page *page)
+struct page *thp_prep(struct page *page)
{
+ if (!page || compound_order(page) == 0)
+ return page;
/*
-* we use page->mapping and page->indexlru in second tail page
+* we use page->mapping and page->index in second tail page
* as list_head: assuming THP order >= 2
*/
+ BUG_ON(compound_order(page) == 1);
INIT_LIST_HEAD(page_deferred_list(page));
set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
+
+ return page;
}
It simplifies the users.
I'm not sure what the simplification is.
If you mean the name change from prep_transhuge_page() to thp_prep(),
that seems fine to me. The following could also be renamed to
thp_prep_device_private_page() or similar.
+void prep_transhuge_device_private_page(struct page *page)
+{
+ prep_compound_page(page, HPAGE_PMD_ORDER);
+ prep_transhuge_page(page);
+ /* Only the head page has a reference to the pgmap. */
+ percpu_ref_put_many(page->pgmap->ref, HPAGE_PMD_NR - 1);
+}
+EXPORT_SYMBOL_GPL(prep_transhuge_device_private_page);
Something else that may interest you from my patch series is support
for page sizes other than PMD_SIZE. I don't know what page sizes
hardware supports. There's no support for page sizes other than PMD
for anonymous memory, so this might not be too useful for you yet.
I did see those changes. It might help some device drivers to do DMA in
larger than PAGE_SIZE blocks but less than PMD_SIZE. It might help
reduce page table sizes since 2MB, 64K, and 4K are commonly supported
GPU page sizes. The MIGRATE_PFN_COMPOUND flag is intended to indicate
that the page size is determined by page_size() so I was thinking ahead
to other than PMD sized pages. However, when migrating a pte_none() or
pmd_none() page, there is no source page to determine the size.
Maybe I need to encode the page order in the migrate PFN entry like
hmm_range_fault().
Anyway, I agree that thinking about page sizes other than PMD is good.
Re: [PATCH v3 1/6] mm/thp: add prep_transhuge_device_private_page()
On Thu, Nov 05, 2020 at 04:51:42PM -0800, Ralph Campbell wrote:
> Add a helper function to allow device drivers to create device private
> transparent huge pages. This is intended to help support device private
> THP migrations.
I think you'd be better off with these calling conventions:
-void prep_transhuge_page(struct page *page)
+struct page *thp_prep(struct page *page)
{
+ if (!page || compound_order(page) == 0)
+ return page;
/*
-* we use page->mapping and page->indexlru in second tail page
+* we use page->mapping and page->index in second tail page
* as list_head: assuming THP order >= 2
*/
+ BUG_ON(compound_order(page) == 1);
INIT_LIST_HEAD(page_deferred_list(page));
set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
+
+ return page;
}
It simplifies the users.
> +void prep_transhuge_device_private_page(struct page *page)
> +{
> + prep_compound_page(page, HPAGE_PMD_ORDER);
> + prep_transhuge_page(page);
> + /* Only the head page has a reference to the pgmap. */
> + percpu_ref_put_many(page->pgmap->ref, HPAGE_PMD_NR - 1);
> +}
> +EXPORT_SYMBOL_GPL(prep_transhuge_device_private_page);
Something else that may interest you from my patch series is support
for page sizes other than PMD_SIZE. I don't know what page sizes your
hardware supports. There's no support for page sizes other than PMD
for anonymous memory, so this might not be too useful for you yet.
Re: [PATCH v3 1/6] mm/thp: add prep_transhuge_device_private_page()
On Thu, Nov 05, 2020 at 04:51:42PM -0800, Ralph Campbell wrote:
> +extern void prep_transhuge_device_private_page(struct page *page);
No need for the extern.
> +static inline void prep_transhuge_device_private_page(struct page *page)
> +{
> +}
Is the code to call this even reachable if THP support is configured
out? If not just declaring it unconditionally and letting dead code
elimination do its job might be a tad cleaner.
> +void prep_transhuge_device_private_page(struct page *page)
I think a kerneldoc comment explaining what this function is useful for
would be helpful.
[PATCH v3 1/6] mm/thp: add prep_transhuge_device_private_page()
Add a helper function to allow device drivers to create device private
transparent huge pages. This is intended to help support device private
THP migrations.
Signed-off-by: Ralph Campbell
---
include/linux/huge_mm.h | 5 +
mm/huge_memory.c| 9 +
2 files changed, 14 insertions(+)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 0365aa97f8e7..3ec26ef27a93 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -184,6 +184,7 @@ extern unsigned long thp_get_unmapped_area(struct file
*filp,
unsigned long flags);
extern void prep_transhuge_page(struct page *page);
+extern void prep_transhuge_device_private_page(struct page *page);
extern void free_transhuge_page(struct page *page);
bool is_transparent_hugepage(struct page *page);
@@ -377,6 +378,10 @@ static inline bool transhuge_vma_suitable(struct
vm_area_struct *vma,
static inline void prep_transhuge_page(struct page *page) {}
+static inline void prep_transhuge_device_private_page(struct page *page)
+{
+}
+
static inline bool is_transparent_hugepage(struct page *page)
{
return false;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 08a183f6c3ab..b4141f12ff31 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -498,6 +498,15 @@ void prep_transhuge_page(struct page *page)
set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
}
+void prep_transhuge_device_private_page(struct page *page)
+{
+ prep_compound_page(page, HPAGE_PMD_ORDER);
+ prep_transhuge_page(page);
+ /* Only the head page has a reference to the pgmap. */
+ percpu_ref_put_many(page->pgmap->ref, HPAGE_PMD_NR - 1);
+}
+EXPORT_SYMBOL_GPL(prep_transhuge_device_private_page);
+
bool is_transparent_hugepage(struct page *page)
{
if (!PageCompound(page))
--
2.20.1
