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SubjectRe: [RFC][PATCH] mm: cut down __GFP_NORETRY page allocation failures
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On Wed, May 4, 2011 at 9:56 AM, Dave Young <hidave.darkstar@gmail.com> wrote:
> 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

unset CONFIG_SCHED_AUTOGROUP and CONFIG_CGROUP_SCHED seems affects the
test results, now I see several nr_alloc_fail (dd is not finished
yet):

dave@darkstar-32:$ grep fail /proc/vmstat:
nr_alloc_fail 4
compact_pagemigrate_failed 0
compact_fail 3
htlb_buddy_alloc_fail 0
thp_collapse_alloc_fail 4

So the result is related to cpu scheduler.

>
>> 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
>



--
Regards
dave
--
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