Messages in this thread |  | | | Date | Thu, 23 Apr 2009 15:59:51 -0700 | | From | Andrew Morton <> | | Subject | Re: [PATCH 15/22] Do not disable interrupts in free_page_mlock() |
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On Wed, 22 Apr 2009 14:53:20 +0100 Mel Gorman <mel@csn.ul.ie> wrote:
> free_page_mlock() tests and clears PG_mlocked using locked versions of the > bit operations. If set, it disables interrupts to update counters and this > happens on every page free even though interrupts are disabled very shortly > afterwards a second time. This is wasteful.
Well. It's only wasteful if the page was mlocked, which is rare.
> This patch splits what free_page_mlock() does. The bit check is still > made. However, the update of counters is delayed until the interrupts are > disabled and the non-lock version for clearing the bit is used. One potential > weirdness with this split is that the counters do not get updated if the > bad_page() check is triggered but a system showing bad pages is getting > screwed already. > > Signed-off-by: Mel Gorman <mel@csn.ul.ie> > Reviewed-by: Christoph Lameter <cl@linux-foundation.org> > Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi> > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> > --- > mm/internal.h | 11 +++-------- > mm/page_alloc.c | 8 +++++++- > 2 files changed, 10 insertions(+), 9 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index 987bb03..58ec1bc 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -157,14 +157,9 @@ static inline void mlock_migrate_page(struct page *newpage, struct page *page) > */ > static inline void free_page_mlock(struct page *page) > { > - if (unlikely(TestClearPageMlocked(page))) { > - unsigned long flags; > - > - local_irq_save(flags); > - __dec_zone_page_state(page, NR_MLOCK); > - __count_vm_event(UNEVICTABLE_MLOCKFREED); > - local_irq_restore(flags); > - } > + __ClearPageMlocked(page); > + __dec_zone_page_state(page, NR_MLOCK); > + __count_vm_event(UNEVICTABLE_MLOCKFREED); > }
The conscientuous reviewer runs around and checks for free_page_mlock() callers in other .c files which might be affected.
Only there are no such callers.
The reviewer's job would be reduced if free_page_mlock() wasn't needlessly placed in a header file!
> #else /* CONFIG_HAVE_MLOCKED_PAGE_BIT */ > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 67cafd0..7f45de1 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -499,7 +499,6 @@ static inline void __free_one_page(struct page *page, > > static inline int free_pages_check(struct page *page) > { > - free_page_mlock(page); > if (unlikely(page_mapcount(page) | > (page->mapping != NULL) | > (page_count(page) != 0) | > @@ -556,6 +555,7 @@ static void __free_pages_ok(struct page *page, unsigned int order) > unsigned long flags; > int i; > int bad = 0; > + int clearMlocked = PageMlocked(page); > > for (i = 0 ; i < (1 << order) ; ++i) > bad += free_pages_check(page + i); > @@ -571,6 +571,8 @@ static void __free_pages_ok(struct page *page, unsigned int order) > kernel_map_pages(page, 1 << order, 0); > > local_irq_save(flags); > + if (unlikely(clearMlocked)) > + free_page_mlock(page);
I wonder what the compiler does in the case CONFIG_HAVE_MLOCKED_PAGE_BIT=n. If it is dumb, this patch would cause additional code generation.
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