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Date: Fri, 30 May 2014 16:10:54 +0530
From: Ritesh Harjani <ritesh.list@...il.com>
To: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Mel Gorman <mgorman@...e.de>,
Laura Abbott <lauraa@...eaurora.org>,
Minchan Kim <minchan@...nel.org>,
Heesub Shin <heesub.shin@...sung.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Michal Nazarewicz <mina86@...a86.com>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Ritesh Harjani <ritesh.harjani@...il.com>,
Nagachandra P <nagachandra@...il.com>
Subject: Re: [PATCH v2 3/3] CMA: always treat free cma pages as non-free on
watermark checking
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@...sung.com>
Date: Wed Jun 12 14:05:02 2013 -0700
On Wed, May 28, 2014 at 12:34 PM, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> commit d95ea5d1('cma: fix watermark checking') introduces ALLOC_CMA flag
> 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@...a86.com>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> 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).
> return false;
> for (o = 0; o < order; o++) {
> /* At the next order, this order's pages become unavailable */
> @@ -2545,10 +2547,6 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> unlikely(test_thread_flag(TIF_MEMDIE))))
> alloc_flags |= ALLOC_NO_WATERMARKS;
> }
> -#ifdef CONFIG_CMA
> - if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> - alloc_flags |= ALLOC_CMA;
> -#endif
> return alloc_flags;
> }
>
> @@ -2818,10 +2816,6 @@ retry_cpuset:
> if (!preferred_zone)
> goto out;
>
> -#ifdef CONFIG_CMA
> - if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> - alloc_flags |= ALLOC_CMA;
> -#endif
> retry:
> /* First allocation attempt */
> page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
> --
> 1.7.9.5
>
> --
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Thanks
Ritesh
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