lkml.org 
[lkml]   [2015]   [Nov]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] vmscan: do not force-scan file lru if its absolute size is small
On Mon 23-11-15 13:39:33, Vladimir Davydov wrote:
> We assume there is enough inactive page cache if the size of inactive
> file lru is greater than the size of active file lru, in which case we
> force-scan file lru ignoring anonymous pages. While this logic works
> fine when there are plenty of page cache pages, it fails if the size of
> file lru is small (several MB): in this case (lru_size >> prio) will be
> 0 for normal scan priorities, as a result, if inactive file lru happens
> to be larger than active file lru, anonymous pages of a cgroup will
> never get evicted unless the system experiences severe memory pressure,
> even if there are gigabytes of unused anonymous memory there, which is
> unfair in respect to other cgroups, whose workloads might be page cache
> oriented.
>
> This patch attempts to fix this by elaborating the "enough inactive page
> cache" check: it makes it not only check that inactive lru size > active
> lru size, but also that we will scan something from the cgroup at the
> current scan priority. If these conditions do not hold, we proceed to
> SCAN_FRACT as usual.

Yes this makes sense. FWIW I have a similar patch waiting for feedback
from testing which catches the other extreme case when we force anon
pages scan without any progress from the kswapd context (I hope I get to
post it soon).

get_scan_count is getting more and more convoluted :/

> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
> Changes in v2:
> - remove unnecessary > 0 (Johannes)
> - elaborate on the comment (Andrew)
>
> mm/vmscan.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bd2918e6391a..97ba9e1cde09 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2043,10 +2043,16 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
> }
>
> /*
> - * There is enough inactive page cache, do not reclaim
> - * anything from the anonymous working set right now.
> + * If there is enough inactive page cache, i.e. if the size of the
> + * inactive list is greater than that of the active list *and* the
> + * inactive list actually has some pages to scan on this priority, we
> + * do not reclaim anything from the anonymous working set right now.
> + * Without the second condition we could end up never scanning an
> + * lruvec even if it has plenty of old anonymous pages unless the
> + * system is under heavy pressure.
> */
> - if (!inactive_file_is_low(lruvec)) {
> + if (!inactive_file_is_low(lruvec) &&
> + get_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
> scan_balance = SCAN_FILE;
> goto out;
> }
> --
> 2.1.4
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

--
Michal Hocko
SUSE Labs


\
 
 \ /
  Last update: 2015-11-23 13:41    [W:0.108 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site