Hi, On Monday, June 02, 2014 09:37:49 AM Ritesh Harjani wrote: > Hi Joonsoo, > > CC'ing the developer of the patch (Tomasz Stanislawski) > > > On Fri, May 30, 2014 at 8:16 PM, Joonsoo Kim <js1304@xxxxxxxxx> wrote: > > 2014-05-30 19:40 GMT+09:00 Ritesh Harjani <ritesh.list@xxxxxxxxx>: > >> Hi Joonsoo, > >> > >> I think you will be loosing the benefit of below patch with your changes. > >> I am no expert here so please bear with me. I tried explaining in the > >> inline comments, let me know if I am wrong. > >> > >> commit 026b08147923142e925a7d0aaa39038055ae0156 > >> Author: Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx> > >> Date: Wed Jun 12 14:05:02 2013 -0700 > > > > Hello, Ritesh. > > > > Thanks for notifying that. > > > >> > >> On Wed, May 28, 2014 at 12:34 PM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote: > >>> commit d95ea5d1('cma: fix watermark checking') introduces ALLOC_CMA flag It is a bit of shame that the author of commit d95ea5d1 (happens to be me :) was not on cc:. > >>> for alloc flag and treats free cma pages as free pages if this flag is > >>> passed to watermark checking. Intention of that patch is that movable page > >>> allocation can be be handled from cma reserved region without starting > >>> kswapd. Now, previous patch changes the behaviour of allocator that > >>> movable allocation uses the page on cma reserved region aggressively, > >>> so this watermark hack isn't needed anymore. Therefore remove it. > >>> > >>> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> > >>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > >>> > >>> diff --git a/mm/compaction.c b/mm/compaction.c > >>> index 627dc2e..36e2fcd 100644 > >>> --- a/mm/compaction.c > >>> +++ b/mm/compaction.c > >>> @@ -1117,10 +1117,6 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist, > >>> > >>> count_compact_event(COMPACTSTALL); > >>> > >>> -#ifdef CONFIG_CMA > >>> - if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE) > >>> - alloc_flags |= ALLOC_CMA; > >>> -#endif > >>> /* Compact each zone in the list */ > >>> for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx, > >>> nodemask) { > >>> diff --git a/mm/internal.h b/mm/internal.h > >>> index 07b6736..a121762 100644 > >>> --- a/mm/internal.h > >>> +++ b/mm/internal.h > >>> @@ -384,7 +384,6 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone, > >>> #define ALLOC_HARDER 0x10 /* try to alloc harder */ > >>> #define ALLOC_HIGH 0x20 /* __GFP_HIGH set */ > >>> #define ALLOC_CPUSET 0x40 /* check for correct cpuset */ > >>> -#define ALLOC_CMA 0x80 /* allow allocations from CMA areas */ > >>> -#define ALLOC_FAIR 0x100 /* fair zone allocation */ > >>> +#define ALLOC_FAIR 0x80 /* fair zone allocation */ > >>> > >>> #endif /* __MM_INTERNAL_H */ > >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >>> index ca678b6..83a8021 100644 > >>> --- a/mm/page_alloc.c > >>> +++ b/mm/page_alloc.c > >>> @@ -1764,20 +1764,22 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark, > >>> long min = mark; > >>> long lowmem_reserve = z->lowmem_reserve[classzone_idx]; > >>> int o; > >>> - long free_cma = 0; > >>> > >>> free_pages -= (1 << order) - 1; > >>> if (alloc_flags & ALLOC_HIGH) > >>> min -= min / 2; > >>> if (alloc_flags & ALLOC_HARDER) > >>> min -= min / 4; > >>> -#ifdef CONFIG_CMA > >>> - /* If allocation can't use CMA areas don't use free CMA pages */ > >>> - if (!(alloc_flags & ALLOC_CMA)) > >>> - free_cma = zone_page_state(z, NR_FREE_CMA_PAGES); > >>> -#endif > >>> + /* > >>> + * We don't want to regard the pages on CMA region as free > >>> + * on watermark checking, since they cannot be used for > >>> + * unmovable/reclaimable allocation and they can suddenly > >>> + * vanish through CMA allocation > >>> + */ > >>> + if (IS_ENABLED(CONFIG_CMA) && z->managed_cma_pages) > >>> + free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES); > >> > >> make this free_cma instead of free_pages. > >> > >>> > >>> - if (free_pages - free_cma <= min + lowmem_reserve) > >>> + if (free_pages <= min + lowmem_reserve) > >> free_pages - free_cma <= min + lowmem_reserve > >> > >> Because in for loop you subtract nr_free which includes the CMA pages. > >> So if you have subtracted NR_FREE_CMA_PAGES > >> from free_pages above then you will be subtracting cma pages again in > >> nr_free (below in for loop). > > > > Yes, I understand the problem you mentioned. > > > > I think that this is complicated issue. > > > > Comit '026b081' you mentioned makes watermark_ok() loose for high order > > allocation compared to kernel that CMA isn't enabled, since free_pages includes > > free_cma pages and most of high order allocation except THP would be > > non-movable allocation. This non-movable allocation can't use cma pages, > > so we shouldn't include free_cma pages. > > > > If most of free cma pages are 0 order, that commit works correctly. We subtract > > nr of free cma pages at the first loop, so there is no problem. But, > > if the system > > have some free high-order cma pages, watermark checking allow high-order > > allocation more easily. > > > > I think that loosing the watermark check is right solution so will takes your > > comment on v2. But I want to know other developer's opinion. > > Thanks for giving this a thought for your v2 patch. > > > > If needed, I can implement to track free_area[o].nr_cma_free and use it for > > precise freepage calculation in watermark check. > > > I guess implementing nr_cma_free would be the correct solution. > Because currently for other than 0 order allocation > we still consider high order free_cma pages as free pages in the for > loop which from the code looks incorrect. > > This can lead to situation when we have more high order free CMA pages > but very less unmovable pages, but zone_watermark returns > ok for unmovable page, thus leading to allocation failure every time > instead of recovering from this situation. > > But its better if experts comment on this. I think that implementing free_area[].nr_cma_free is a correct long-term solution and it should be done before the current patch gets applied. [ Tomasz is on holiday currently but he should be back tomorrow so he can also take a look at the issue. ] Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>