linux-kernel - Re: [PATCH] vmscan: check all_unreclaimable in direct reclaim path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <AANLkTi=4kwu0Y5-MDye3TD+zZiku62NtNCMtWLn==p12@mail.gmail.com>
Date:	Fri, 10 Sep 2010 16:24:00 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"M. Vefa Bicakci" <bicave@...eronline.com>, stable@...nel.org
Subject: Re: [PATCH] vmscan: check all_unreclaimable in direct reclaim path

On Thu, Sep 9, 2010 at 6:19 AM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Thu, 9 Sep 2010 00:45:27 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> +static inline bool zone_reclaimable(struct zone *zone)
>> +{
>> +     return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
>> +}
>> +
>> +static inline bool all_unreclaimable(struct zonelist *zonelist,
>> +             struct scan_control *sc)
>> +{
>> +     struct zoneref *z;
>> +     struct zone *zone;
>> +     bool all_unreclaimable = true;
>> +
>> +     if (!scanning_global_lru(sc))
>> +             return false;
>> +
>> +     for_each_zone_zonelist_nodemask(zone, z, zonelist,
>> +                     gfp_zone(sc->gfp_mask), sc->nodemask) {
>> +             if (!populated_zone(zone))
>> +                     continue;
>> +             if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
>> +                     continue;
>> +             if (zone_reclaimable(zone)) {
>> +                     all_unreclaimable = false;
>> +                     break;
>> +             }
>> +     }
>> +
>>       return all_unreclaimable;
>>  }
>
> Could we have some comments over these functions please?  Why they
> exist, what problem they solve, how they solve them, etc.  Stuff which
> will be needed for maintaining this code three years from now.
>
> We may as well remove the `inline's too.  gcc will tkae care of that.
>
>> -             if (nr_slab == 0 &&
>> -                zone->pages_scanned >= (zone_reclaimable_pages(zone) * 6))
>> +             if (nr_slab == 0 && !zone_reclaimable(zone))
>
> Extra marks for working out and documenting how we decided on the value
> of "6".  Sigh.  It's hopefully in the git record somewhere.

Here it is (necessary to add additional comment?):

commit 4ff1ffb4870b007b86f21e5f27eeb11498c4c077
Author: Nick Piggin <npiggin@...e.de>
Date:   Mon Sep 25 23:31:28 2006 -0700

    [PATCH] oom: reclaim_mapped on oom

    Potentially it takes several scans of the lru lists before we can even start
    reclaiming pages.

    mapped pages, with young ptes can take 2 passes on the active list + one on
    the inactive list.  But reclaim_mapped may not always kick in
instantly, so it
    could take even more than that.

    Raise the threshold for marking a zone as all_unreclaimable from a
factor of 4
    time the pages in the zone to 6.  Introduce a mechanism to force
    reclaim_mapped if we've reached a factor 3 and still haven't made progress.

    Previously, a customer doing stress testing was able to easily OOM the box
    after using only a small fraction of its swap (~100MB).  After the
patches, it
    would only OOM after having used up all swap (~800MB).

>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
>
>



-- 
Regards
dave
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/