Messages in this thread | | | Date | Thu, 26 Jan 2006 15:55:13 +0000 (GMT) | From | Mel Gorman <> | Subject | Re: [PATCH 2/4] Split the free lists into kernel and user parts |
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On Mon, 23 Jan 2006, Marcelo Tosatti wrote:
> On Mon, Jan 23, 2006 at 09:39:16AM +0000, Mel Gorman wrote: > > On Sun, 22 Jan 2006, Marcelo Tosatti wrote: > > > > > Hi Mel, > > > > > > On Fri, Jan 20, 2006 at 11:54:55AM +0000, Mel Gorman wrote: > > > > > > > > This patch adds the core of the anti-fragmentation strategy. It works by > > > > grouping related allocation types together. The idea is that large groups of > > > > pages that may be reclaimed are placed near each other. The zone->free_area > > > > list is broken into RCLM_TYPES number of lists. > > > > > > > > Signed-off-by: Mel Gorman <mel@csn.ul.ie> > > > > Signed-off-by: Joel Schopp <jschopp@austin.ibm.com> > > > > diff -rup -X /usr/src/patchset-0.5/bin//dontdiff linux-2.6.16-rc1-mm1-001_antifrag_flags/include/linux/mmzone.h linux-2.6.16-rc1-mm1-002_fragcore/include/linux/mmzone.h > > > > --- linux-2.6.16-rc1-mm1-001_antifrag_flags/include/linux/mmzone.h 2006-01-19 11:21:59.000000000 +0000 > > > > +++ linux-2.6.16-rc1-mm1-002_fragcore/include/linux/mmzone.h 2006-01-19 21:51:05.000000000 +0000 > > > > @@ -22,8 +22,16 @@ > > > > #define MAX_ORDER CONFIG_FORCE_MAX_ZONEORDER > > > > #endif > > > > > > > > +#define RCLM_NORCLM 0 > > > > +#define RCLM_EASY 1 > > > > +#define RCLM_TYPES 2 > > > > + > > > > +#define for_each_rclmtype_order(type, order) \ > > > > + for (order = 0; order < MAX_ORDER; order++) \ > > > > + for (type = 0; type < RCLM_TYPES; type++) > > > > + > > > > struct free_area { > > > > - struct list_head free_list; > > > > + struct list_head free_list[RCLM_TYPES]; > > > > unsigned long nr_free; > > > > }; > > > > > > > > diff -rup -X /usr/src/patchset-0.5/bin//dontdiff linux-2.6.16-rc1-mm1-001_antifrag_flags/include/linux/page-flags.h linux-2.6.16-rc1-mm1-002_fragcore/include/linux/page-flags.h > > > > --- linux-2.6.16-rc1-mm1-001_antifrag_flags/include/linux/page-flags.h 2006-01-19 11:21:59.000000000 +0000 > > > > +++ linux-2.6.16-rc1-mm1-002_fragcore/include/linux/page-flags.h 2006-01-19 21:51:05.000000000 +0000 > > > > @@ -76,6 +76,7 @@ > > > > #define PG_reclaim 17 /* To be reclaimed asap */ > > > > #define PG_nosave_free 18 /* Free, should not be written */ > > > > #define PG_uncached 19 /* Page has been mapped as uncached */ > > > > +#define PG_easyrclm 20 /* Page is in an easy reclaim block */ > > > > > > > > /* > > > > * Global page accounting. One instance per CPU. Only unsigned longs are > > > > @@ -345,6 +346,12 @@ extern void __mod_page_state_offset(unsi > > > > #define SetPageUncached(page) set_bit(PG_uncached, &(page)->flags) > > > > #define ClearPageUncached(page) clear_bit(PG_uncached, &(page)->flags) > > > > > > > > +#define PageEasyRclm(page) test_bit(PG_easyrclm, &(page)->flags) > > > > +#define SetPageEasyRclm(page) set_bit(PG_easyrclm, &(page)->flags) > > > > +#define ClearPageEasyRclm(page) clear_bit(PG_easyrclm, &(page)->flags) > > > > +#define __SetPageEasyRclm(page) __set_bit(PG_easyrclm, &(page)->flags) > > > > +#define __ClearPageEasyRclm(page) __clear_bit(PG_easyrclm, &(page)->flags) > > > > + > > > > > > You can't read/write to page->flags non-atomically, except when you > > > guarantee that the page is not visible to other CPU's (eg at the very > > > end of the page freeing code). > > > > > > > The helper PageEasyRclm is only used when either the spinlock is held or a > > per-cpu page is being released so it should be safe. The Set and Clear > > helpers are only used with a spinlock held. > > Mel, > > Other codepaths which touch page->flags do not hold any lock, so you > really must use atomic operations, except when you've guarantee that the > page is being freed and won't be reused. >
Understood, so I took another look to be sure;
PageEasyRclm() is used on pages that are about to be freed to the main or per-cpu allocator so it should be safe.
__SetPageEasyRclm is called when the page is about to be freed. It should be safe from concurrent access.
__ClearPageEasyRclm is called when the page is about to be allocated. It should be safe.
I think it is guaranteed that there are on concurrent accessing of the page flags. Is there something I have missed?
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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