lkml.org 
[lkml]   [2012]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH] mm,vmscan: free pages if compaction_suitable tells us to
    On Sun, Nov 25, 2012 at 01:29:50PM -0500, Rik van Riel wrote:
    > On Sun, 25 Nov 2012 17:57:28 +0100
    > Johannes Hirte <johannes.hirte@fem.tu-ilmenau.de> wrote:
    >
    > > With kernel 3.7-rc6 I've still problems with kswapd0 on my laptop
    >
    > > And this is most of the time. I've only observed this behavior on the
    > > laptop. Other systems don't show this.
    >
    > This suggests it may have something to do with small memory zones,
    > where we end up with the "funny" situation that the high watermark
    > (+ balance gap) for a particular zone is less than the low watermark
    > + 2<<order pages, which is the number of free pages required to keep
    > compaction_suitable happy.
    >
    > Could you try this patch?

    It's not quite enough because it's not reaching the conditions you
    changed, see analysis in https://lkml.org/lkml/2012/11/20/567

    But even fixing it up (by adding the compaction_suitable() test in
    this preliminary scan over the zones and setting end_zone accordingly)
    is not enough because no actual reclaim happens at priority 12 in a
    small zone. So the number of free pages is not actually changing and
    the compaction_suitable() checks keep the loop going.

    The problem is fairly easy to reproduce, by the way. Just boot with
    mem=800M to have a relatively small lowmem reserve in the DMA zone.
    Fill it up with page cache, then allocate transparent huge pages.

    With your patch and my fix to the preliminary zone loop, there won't
    be any hung task warnings anymore because kswapd actually calls
    shrink_slab() and there is a rescheduling point in there, but it still
    loops forever.

    It also seems a bit aggressive to try to balance a small zone like DMA
    for a huge page when it's not a GFP_DMA allocation, but none of these
    checks actually take the classzone into account. Do we have any
    agreement over what this whole thing is supposed to be doing?

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index b99ecba..f7e54df 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -2412,6 +2412,9 @@ static void age_active_anon(struct zone *zone, struct scan_control *sc)
    * would need to be at least 256M for it to be balance a whole node.
    * Similarly, on x86-64 the Normal zone would need to be at least 1G
    * to balance a node on its own. These seemed like reasonable ratios.
    + *
    + * The kswapd source code is brought to you by Advil®. "For today's
    + * tough pain, one might not be enough."
    */
    static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
    int classzone_idx)
    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/
    \
     
     \ /
      Last update: 2012-11-26 00:01    [W:6.865 / U:0.092 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site