Messages in this thread | | | Subject | Re: [PATCH 02/28] mm, page_alloc: Use new PageAnonHead helper in the free page fast path | From | Vlastimil Babka <> | Date | Mon, 25 Apr 2016 11:56:19 +0200 |
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On 04/15/2016 10:58 AM, Mel Gorman wrote: > The PageAnon check always checks for compound_head but this is a relatively > expensive check if the caller already knows the page is a head page. This > patch creates a helper and uses it in the page free path which only operates > on head pages. > > With this patch and "Only check PageCompound for high-order pages", the > performance difference on a page allocator microbenchmark is; > [...] > > There is a sizable boost to the free allocator performance. While there > is an apparent boost on the allocation side, it's likely a co-incidence > or due to the patches slightly reducing cache footprint. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
This again highlights the cost of thp rework due to those compound_head() calls, and a more general solution would benefit other places, but this can always be converted later if such solution happens.
> --- > include/linux/page-flags.h | 7 ++++++- > mm/page_alloc.c | 2 +- > 2 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index f4ed4f1b0c77..ccd04ee1ba2d 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -371,10 +371,15 @@ PAGEFLAG(Idle, idle, PF_ANY) > #define PAGE_MAPPING_KSM 2 > #define PAGE_MAPPING_FLAGS (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM) > > +static __always_inline int PageAnonHead(struct page *page) > +{ > + return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0; > +} > + > static __always_inline int PageAnon(struct page *page) > { > page = compound_head(page); > - return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0; > + return PageAnonHead(page); > } > > #ifdef CONFIG_KSM > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 5d205bcfe10d..6812de41f698 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1048,7 +1048,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order) > bad += free_pages_check(page + i); > } > } > - if (PageAnon(page)) > + if (PageAnonHead(page)) > page->mapping = NULL; > bad += free_pages_check(page); > if (bad) >
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