Messages in this thread | | | Date | Fri, 30 May 2014 16:59:18 +0200 | From | Vlastimil Babka <> | Subject | Re: MIGRATE_RESERVE pages in show_mem function problems |
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On 05/28/2014 04:24 AM, Wang, Yalin wrote: > Hi > > I find the show_mem function show page MIGRATE types result is not correct for > MIGRATE_RESERVE pages : > > Normal: 1582*4kB (UEMC) 1317*8kB (UEMC) 1020*16kB (UEMC) 450*32kB (UEMC) 206*64kB (UEMC) 40*128kB (UM) 10*256kB (UM) 10*512kB (UM) 1*1024kB (M) 0*2048kB 0*4096kB = 74592kB > > Some pages should be marked (R) , while it is changed into MIGRATE_MOVEABLE or UNMOVEABLE in free_area list , > It's not correct for debug . > I make a patch for this: > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 5dba293..6ef8ebe 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1198,7 +1198,8 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order, > list_add_tail(&page->lru, list); > if (IS_ENABLED(CONFIG_CMA)) { > mt = get_pageblock_migratetype(page); > - if (!is_migrate_cma(mt) && !is_migrate_isolate(mt)) > + if (!is_migrate_cma(mt) && !is_migrate_isolate(mt) > + && mt != MIGRATE_RESERVE) > mt = migratetype; > } > set_freepage_migratetype(page, mt); > > > seems work ok , I am curious is it a BUG ? or designed like this for some reason ?
Hi, this is a known problem that should be fixed for the rmqueue_bulk() part by this patch: http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-prevent-migrate_reserve-pages-from-being-misplaced.patch
Testing is welcome if you can reproduce it easily enough.
Note that even with the patch, MIGRATE_RESERVE pageblocks can still disappear for two reasons:
- when MAX_ORDER-1 > pageblock_order (such as x86_64), there can be a single MIGRATE_RESERVE pageblock created for a smaller zone, and get merged with !MIGRATE_RESERVE buddy pageblock - when min_free_kbytes sysctl is used, creation of new MIGRATE_RESERVE pageblocks can race with other CPUs putting pages in their pcplists, and then freeing then on a wronge free_list. If try_to_steal_freepages happens to find such misplaced page, it might remark the pageblock.
I think the second problem is extremely rare, but Joonsoo Kim confirmed the first one to happen. You can check the -mm archives for threads around the patch above.
Vlastimil
> Thanks > > > <6>[ 250.751554] lowmem_reserve[]: 0 0 0 > <6>[ 250.751606] Normal: 1582*4kB (UEMC) 1317*8kB (UEMC) 1020*16kB (UEMC) 450*32kB (UEMC) 206*64kB (UEMC) 40*128kB (UM) 10*256kB (UM) 10*512kB (UM) 1*1024kB (M) 0*2048kB 0*4096kB = 74592kB > <6>[ 250.751848] HighMem: 167*4kB (UC) 3*8kB (U) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 692kB > <6>[ 250.752020] 62596 total pagecache pages > <6>[ 250.752046] 0 pages in swap cache > <6>[ 250.752074] Swap cache stats: add 0, delete 0, find 0/0 > > > > > Sony Mobile Communications > Tel: My Number +18610323092 > yalin.wang@sonymobile.com > sonymobile.com > > > > -- > 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=ilto:"dont@kvack.org"> email@kvack.org </a> >
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