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Message-Id: <E270108E-B7EC-4A12-9662-4CF1CC7B69DE@gmail.com>
Date: Fri, 21 Dec 2012 21:04:37 +0800
From: lihanhui <hanhui.li@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Michal Nazarewicz <mina86@...a86.com>,
Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 2/2] mm: support MIGRATE_DISCARD
在 2012-9-5，下午4:11，Minchan Kim <minchan@...nel.org> 写道：
> This patch introudes MIGRATE_DISCARD mode in migration.
> It drops *clean cache pages* instead of migration so that
> migration latency could be reduced by avoiding (memcpy + page remapping).
> It's useful for CMA because latency of migration is very important rather
> than eviction of background processes's workingset. In addition, it needs
> less free pages for migration targets so it could avoid memory reclaiming
> to get free pages, which is another factor increase latency.
>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Michal Nazarewicz <mina86@...a86.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> include/linux/migrate_mode.h | 7 +++++++
> mm/migrate.c | 41 ++++++++++++++++++++++++++++++++++++++---
> mm/page_alloc.c | 2 +-
> 3 files changed, 46 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
> index 8848cad..4eb1646 100644
> --- a/include/linux/migrate_mode.h
> +++ b/include/linux/migrate_mode.h
> @@ -14,6 +14,13 @@
> */
> #define MIGRATE_SYNC ((__force migrate_mode_t)0x4)
>
> +/*
> + * MIGRTATE_DISCARD will discard clean cache page instead of migration.
> + * MIGRATE_ASYNC, MIGRATE_SYNC_LIGHT, MIGRATE_SYNC shouldn't be used
> + * together with OR flag in current implementation.
> + */
> +#define MIGRATE_DISCARD ((__force migrate_mode_t)0x8)
> +
> typedef unsigned __bitwise__ migrate_mode_t;
>
> #endif /* MIGRATE_MODE_H_INCLUDED */
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 28d464b..2de7709 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -678,6 +678,19 @@ static int move_to_new_page(struct page *newpage, struct page *page,
> return rc;
> }
>
> +static int discard_page(struct page *page)
> +{
> + int ret = -EAGAIN;
> +
> + struct address_space *mapping = page_mapping(page);
> + if (page_has_private(page))
> + if (!try_to_release_page(page, GFP_KERNEL))
> + return ret;
> + if (remove_mapping(mapping, page))
> + ret = 0;
> + return ret;
> +}
> +
> static int __unmap_and_move(struct page *page, struct page *newpage,
> int force, bool offlining, migrate_mode_t mode)
> {
> @@ -685,6 +698,9 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> int remap_swapcache = 1;
> struct mem_cgroup *mem;
> struct anon_vma *anon_vma = NULL;
> + enum ttu_flags ttu_flags;
> + bool discard_mode = false;
> + bool file = false;
>
> if (!trylock_page(page)) {
> if (!force || (mode & MIGRATE_ASYNC))
> @@ -799,12 +815,31 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> goto skip_unmap;
> }
>
> + file = page_is_file_cache(page);
> + ttu_flags = TTU_IGNORE_ACCESS;
> +retry:
> + if (!(mode & MIGRATE_DISCARD) || !file || PageDirty(page))
> + ttu_flags |= (TTU_MIGRATION | TTU_IGNORE_MLOCK);
> + else
> + discard_mode = true;
> +
> /* Establish migration ptes or remove ptes */
> - try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
> + rc = try_to_unmap(page, ttu_flags);
>
> skip_unmap:
> - if (!page_mapped(page))
> - rc = move_to_new_page(newpage, page, remap_swapcache, mode);
> + if (rc == SWAP_SUCCESS) {
> + if (!discard_mode) {
> + rc = move_to_new_page(newpage, page,
> + remap_swapcache, mode);
> + } else {
> + rc = discard_page(page);
> + goto uncharge;
> + }
> + } else if (rc == SWAP_MLOCK && discard_mode) {
> + mode &= ~MIGRATE_DISCARD;
> + discard_mode = false;
> + goto retry;
> + }
>
> if (rc && remap_swapcache)
> remove_migration_ptes(page, page);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ba3100a..e14b960 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5670,7 +5670,7 @@ static int __alloc_contig_migrate_range(unsigned long start, unsigned long end)
>
> ret = migrate_pages(&cc.migratepages,
> __alloc_contig_migrate_alloc,
> - 0, false, MIGRATE_SYNC);
> + 0, false, MIGRATE_SYNC|MIGRATE_DISCARD);
> }
>
> putback_lru_pages(&cc.migratepages);
> --
> 1.7.9.5
>
> --
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