Re: [RFC][PATCH] mm: cut down __GFP_NORETRY page allocation failures

[Dave Young <hidave.darkstar@gmail.com>]

On Thu, Apr 28, 2011 at 9:36 PM, Wu Fengguang <fengguang.wu@intel.com> wrote:
> Concurrent page allocations are suffering from high failure rates.
>
> On a 8p, 3GB ram test box, when reading 1000 sparse files of size 1GB,
> the page allocation failures are
>
> nr_alloc_fail 733       # interleaved reads by 1 single task
> nr_alloc_fail 11799     # concurrent reads by 1000 tasks
>
> The concurrent read test script is:
>
>        for i in `seq 1000`
>        do
>                truncate -s 1G /fs/sparse-$i
>                dd if=/fs/sparse-$i of=/dev/null &
>        done
>

With Core2 Duo, 3G ram, No swap partition I can not produce the alloc fail

> In order for get_page_from_freelist() to get free page,
>
> (1) try_to_free_pages() should use much higher .nr_to_reclaim than the
>    current SWAP_CLUSTER_MAX=32, in order to draw the zone out of the
>    possible low watermark state as well as fill the pcp with enough free
>    pages to overflow its high watermark.
>
> (2) the get_page_from_freelist() _after_ direct reclaim should use lower
>    watermark than its normal invocations, so that it can reasonably
>    "reserve" some free pages for itself and prevent other concurrent
>    page allocators stealing all its reclaimed pages.
>
> Some notes:
>
> - commit 9ee493ce ("mm: page allocator: drain per-cpu lists after direct
>  reclaim allocation fails") has the same target, however is obviously
>  costly and less effective. It seems more clean to just remove the
>  retry and drain code than to retain it.
>
> - it's a bit hacky to reclaim more than requested pages inside
>  do_try_to_free_page(), and it won't help cgroup for now
>
> - it only aims to reduce failures when there are plenty of reclaimable
>  pages, so it stops the opportunistic reclaim when scanned 2 times pages
>
> Test results:
>
> - the failure rate is pretty sensible to the page reclaim size,
>  from 282 (WMARK_HIGH) to 704 (WMARK_MIN) to 10496 (SWAP_CLUSTER_MAX)
>
> - the IPIs are reduced by over 100 times
>
> base kernel: vanilla 2.6.39-rc3 + __GFP_NORETRY readahead page allocation patch
> -------------------------------------------------------------------------------
> nr_alloc_fail 10496
> allocstall 1576602
>
> slabs_scanned 21632
> kswapd_steal 4393382
> kswapd_inodesteal 124
> kswapd_low_wmark_hit_quickly 885
> kswapd_high_wmark_hit_quickly 2321
> kswapd_skip_congestion_wait 0
> pageoutrun 29426
>
> CAL:     220449     220246     220372     220558     220251     219740     220043     219968   Function call interrupts
>
> LOC:     536274     532529     531734     536801     536510     533676     534853     532038   Local timer interrupts
> RES:       3032       2128       1792       1765       2184       1703       1754       1865   Rescheduling interrupts
> TLB:        189         15         13         17         64        294         97         63   TLB shootdowns

Could you tell how to get above info?

>
> patched (WMARK_MIN)
> -------------------
> nr_alloc_fail 704
> allocstall 105551
>
> slabs_scanned 33280
> kswapd_steal 4525537
> kswapd_inodesteal 187
> kswapd_low_wmark_hit_quickly 4980
> kswapd_high_wmark_hit_quickly 2573
> kswapd_skip_congestion_wait 0
> pageoutrun 35429
>
> CAL:         93        286        396        754        272        297        275        281   Function call interrupts
>
> LOC:     520550     517751     517043     522016     520302     518479     519329     517179   Local timer interrupts
> RES:       2131       1371       1376       1269       1390       1181       1409       1280   Rescheduling interrupts
> TLB:        280         26         27         30         65        305        134         75   TLB shootdowns
>
> patched (WMARK_HIGH)
> --------------------
> nr_alloc_fail 282
> allocstall 53860
>
> slabs_scanned 23936
> kswapd_steal 4561178
> kswapd_inodesteal 0
> kswapd_low_wmark_hit_quickly 2760
> kswapd_high_wmark_hit_quickly 1748
> kswapd_skip_congestion_wait 0
> pageoutrun 32639
>
> CAL:         93        463        410        540        298        282        272        306   Function call interrupts
>
> LOC:     513956     510749     509890     514897     514300     512392     512825     510574   Local timer interrupts
> RES:       1174       2081       1411       1320       1742       2683       1380       1230   Rescheduling interrupts
> TLB:        274         21         19         22         57        317        131         61   TLB shootdowns
>
> this patch (WMARK_HIGH, limited scan)
> -------------------------------------
> nr_alloc_fail 276
> allocstall 54034
>
> slabs_scanned 24320
> kswapd_steal 4507482
> kswapd_inodesteal 262
> kswapd_low_wmark_hit_quickly 2638
> kswapd_high_wmark_hit_quickly 1710
> kswapd_skip_congestion_wait 0
> pageoutrun 32182
>
> CAL:         69        443        421        567        273        279        269        334   Function call interrupts
>
> LOC:     514736     511698     510993     514069     514185     512986     513838     511229   Local timer interrupts
> RES:       2153       1556       1126       1351       3047       1554       1131       1560   Rescheduling interrupts
> TLB:        209         26         20         15         71        315        117         71   TLB shootdowns
>
> CC: Mel Gorman <mel@linux.vnet.ibm.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
>  mm/page_alloc.c |   17 +++--------------
>  mm/vmscan.c     |    6 ++++++
>  2 files changed, 9 insertions(+), 14 deletions(-)
> --- linux-next.orig/mm/vmscan.c 2011-04-28 21:16:16.000000000 +0800
> +++ linux-next/mm/vmscan.c      2011-04-28 21:28:57.000000000 +0800
> @@ -1978,6 +1978,8 @@ static void shrink_zones(int priority, s
>                                continue;
>                        if (zone->all_unreclaimable && priority != DEF_PRIORITY)
>                                continue;       /* Let kswapd poll it */
> +                       sc->nr_to_reclaim = max(sc->nr_to_reclaim,
> +                                               zone->watermark[WMARK_HIGH]);
>                }
>
>                shrink_zone(priority, zone, sc);
> @@ -2034,6 +2036,7 @@ static unsigned long do_try_to_free_page
>        struct zoneref *z;
>        struct zone *zone;
>        unsigned long writeback_threshold;
> +       unsigned long min_reclaim = sc->nr_to_reclaim;
>
>        get_mems_allowed();
>        delayacct_freepages_start();
> @@ -2067,6 +2070,9 @@ static unsigned long do_try_to_free_page
>                        }
>                }
>                total_scanned += sc->nr_scanned;
> +               if (sc->nr_reclaimed >= min_reclaim &&
> +                   total_scanned > 2 * sc->nr_to_reclaim)
> +                       goto out;
>                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
>                        goto out;
>
> --- linux-next.orig/mm/page_alloc.c     2011-04-28 21:16:16.000000000 +0800
> +++ linux-next/mm/page_alloc.c  2011-04-28 21:16:18.000000000 +0800
> @@ -1888,9 +1888,8 @@ __alloc_pages_direct_reclaim(gfp_t gfp_m
>        nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
>        int migratetype, unsigned long *did_some_progress)
>  {
> -       struct page *page = NULL;
> +       struct page *page;
>        struct reclaim_state reclaim_state;
> -       bool drained = false;
>
>        cond_resched();
>
> @@ -1912,22 +1911,12 @@ __alloc_pages_direct_reclaim(gfp_t gfp_m
>        if (unlikely(!(*did_some_progress)))
>                return NULL;
>
> -retry:
> +       alloc_flags |= ALLOC_HARDER;
> +
>        page = get_page_from_freelist(gfp_mask, nodemask, order,
>                                        zonelist, high_zoneidx,
>                                        alloc_flags, preferred_zone,
>                                        migratetype);
> -
> -       /*
> -        * If an allocation failed after direct reclaim, it could be because
> -        * pages are pinned on the per-cpu lists. Drain them and try again
> -        */
> -       if (!page && !drained) {
> -               drain_all_pages();
> -               drained = true;
> -               goto retry;
> -       }
> -
>        return page;
>  }
>
>



-- 
Regards
dave