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Date: Fri, 27 Mar 2009 15:30:35 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Johannes Weiner <hannes@...xchg.org>,
MinChan Kim <minchan.kim@...il.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Rafael J. Wysocki" <rjw@...k.pl>, Rik van Riel <riel@...hat.com>,
Balbir Singh <balbir@...ibm.com>
Subject: Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan:
rename sc.may_swap to may_unmap)
On Fri, 27 Mar 2009 15:19:26 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> Added
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Balbir Singh <balbir@...ibm.com>
>
> I'm sorry for replying to a very old mail.
>
> > @@ -1713,7 +1713,7 @@ unsigned long try_to_free_mem_cgroup_pag
> > {
> > struct scan_control sc = {
> > .may_writepage = !laptop_mode,
> > - .may_swap = 1,
> > + .may_unmap = 1,
> > .swap_cluster_max = SWAP_CLUSTER_MAX,
> > .swappiness = swappiness,
> > .order = 0,
> > @@ -1723,7 +1723,7 @@ unsigned long try_to_free_mem_cgroup_pag
> > struct zonelist *zonelist;
> >
> > if (noswap)
> > - sc.may_swap = 0;
> > + sc.may_unmap = 0;
> >
> > sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
> > (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
> IIUC, memcg had used may_swap as a flag for "we need to use swap?" as the name indicate.
>
> Because, when mem+swap hits the limit, trying to swapout pages is meaningless
> as it doesn't change mem+swap usage.
>
Good catch...sigh, I missed this disussion.
> What do you think of this patch?
> ===
> From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
>
> vmscan-rename-scmay_swap-to-may_unmap.patch removed may_swap flag,
> but memcg had used it as a flag for "we need to use swap?", as the
> name indicate.
>
> And in current implementation, memcg cannot reclaim mapped file caches
> when mem+swap hits the limit.
>
When mem+swap hits the limit, swap-out anonymous page doesn't reduce the
amount of usage of mem+swap, so, swap-out should be avoided.
> re-introduce may_swap flag and handle it at shrink_page_list.
>
> This patch doesn't influence any scan_control users other than memcg.
>
> Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Seems good,
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
But hum....Maybe this lru scan work in the same way as the case
of !total_swap_pages. (means don't scan anon LRU.)
revisit this later.
-Kame
> ---
> mm/vmscan.c | 15 ++++++++++++++-
> 1 files changed, 14 insertions(+), 1 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c815653..86118d9 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -64,6 +64,9 @@ struct scan_control {
> /* Can mapped pages be reclaimed? */
> int may_unmap;
>
> + /* Can pages be swapped as part of reclaim? */
> + int may_swap;
> +
> /* This context's SWAP_CLUSTER_MAX. If freeing memory for
> * suspend, we effectively ignore SWAP_CLUSTER_MAX.
> * In this context, it doesn't matter that we scan the
> @@ -616,6 +619,11 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> if (!sc->may_unmap && page_mapped(page))
> goto keep_locked;
>
> + if (!sc->may_swap && PageSwapBacked(page)
> + /* SwapCache uses 'swap' already */
> + && !PageSwapCache(page))
> + goto keep_locked;
> +
> /* Double the slab pressure for mapped and swapcache pages */
> if (page_mapped(page) || PageSwapCache(page))
> sc->nr_scanned++;
> @@ -1696,6 +1704,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> .may_writepage = !laptop_mode,
> .swap_cluster_max = SWAP_CLUSTER_MAX,
> .may_unmap = 1,
> + .may_swap = 1,
> .swappiness = vm_swappiness,
> .order = order,
> .mem_cgroup = NULL,
> @@ -1715,6 +1724,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
> struct scan_control sc = {
> .may_writepage = !laptop_mode,
> .may_unmap = 1,
> + .may_swap = 1,
> .swap_cluster_max = SWAP_CLUSTER_MAX,
> .swappiness = swappiness,
> .order = 0,
> @@ -1724,7 +1734,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
> struct zonelist *zonelist;
>
> if (noswap)
> - sc.may_unmap = 0;
> + sc.may_swap = 0;
>
> sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
> (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
> @@ -1764,6 +1774,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
> struct scan_control sc = {
> .gfp_mask = GFP_KERNEL,
> .may_unmap = 1,
> + .may_swap = 1,
> .swap_cluster_max = SWAP_CLUSTER_MAX,
> .swappiness = vm_swappiness,
> .order = order,
> @@ -2110,6 +2121,7 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
> struct scan_control sc = {
> .gfp_mask = GFP_KERNEL,
> .may_unmap = 0,
> + .may_swap = 1,
> .may_writepage = 1,
> .isolate_pages = isolate_pages_global,
> };
> @@ -2292,6 +2304,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> struct scan_control sc = {
> .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
> .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
> + .may_swap = 1,
> .swap_cluster_max = max_t(unsigned long, nr_pages,
> SWAP_CLUSTER_MAX),
> .gfp_mask = gfp_mask,
>
--
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