[PATCH] mm: Remove redundant PageMemcgKmem(page) call

[PATCH] mm: Remove redundant PageMemcgKmem(page) call

[Shengken Lin]

The function of PageMemcgKmem(page) is the same as that of
folio_memcg_kmem(folio).

Since __memcg_kmem_uncharge_page already uses folio_memcg_kmem to check
if a folio has been uncharged, calling PageMemcgKmem(page) before
__memcg_kmem_uncharge_page is redundant.

Signed-off-by: Shengken Lin <shengken.lin@amlogic.com>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 579789600a3c..5a76760de495 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1055,7 +1055,7 @@ __always_inline bool free_pages_prepare(struct page *page,
 	trace_mm_page_free(page, order);
 	kmsan_free_page(page, order);

-	if (memcg_kmem_online() && PageMemcgKmem(page))
+	if (memcg_kmem_online())
 		__memcg_kmem_uncharge_page(page, order);

 	/*
--
2.34.1

Re: [PATCH] mm: Remove redundant PageMemcgKmem(page) call

[Matthew Wilcox]

On Wed, Feb 12, 2025 at 10:06:27AM +0800, Shengken Lin wrote:
> The function of PageMemcgKmem(page) is the same as that of
> folio_memcg_kmem(folio).
> 
> Since __memcg_kmem_uncharge_page already uses folio_memcg_kmem to check
> if a folio has been uncharged, calling PageMemcgKmem(page) before
> __memcg_kmem_uncharge_page is redundant.

But it saves a function call.  NAK.

Re: Re: [PATCH] mm: Remove redundant PageMemcgKmem(page) call

[Shengken.Lin]

[-- Attachment #1: Type: text/plain, Size: 1073 bytes --]

On Wed, 12 Feb 2025 04:28PM +0000, Matthew Wilcox wrote:
>On Wed, Feb 12, 2025 at 10:06:27AM +0800, Shengken Lin wrote:
>> The function of PageMemcgKmem(page) is the same as that of
>> folio_memcg_kmem(folio).
>> 
>> Since __memcg_kmem_uncharge_page already uses folio_memcg_kmem to check
>> if a folio has been uncharged, calling PageMemcgKmem(page) before
>> __memcg_kmem_uncharge_page is redundant.
>
>But it saves a function call.  NAK.
Hi Matthew Wilcox,
If it can save a function call, then adding PageMemcgKmem(page)
in include/linux/memcontrol.h would make the code more consistent.
If this is considered more reasonable, I can submit a new patch.
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1707,7 +1707,7 @@ static inline int memcg_kmem_charge_page(struct page *page, gfp_t gfp,
 
 static inline void memcg_kmem_uncharge_page(struct page *page, int order)
 {
-       if (memcg_kmem_online())
+       if (memcg_kmem_online() && PageMemcgKmem(page))
                __memcg_kmem_uncharge_page(page, order);
 }
--
Best regards,
Shengken Lin

[-- Attachment #2: Type: text/html, Size: 1718 bytes --]

Re: Re: [PATCH] mm: Remove redundant PageMemcgKmem(page) call

[Matthew Wilcox]

On Thu, Feb 20, 2025 at 05:47:56PM +0800, Shengken.Lin@amlogic.com wrote:
> If it can save a function call, then adding PageMemcgKmem(page)
> in include/linux/memcontrol.h would make the code more consistent.

The code is fine the way it is.