Re: [PATCH v2] page_alloc: consider highatomic reserve in wmartermark fast
From: Jaewon Kim
Date: Sat Jun 13 2020 - 09:09:10 EST
2020ë 6ì 13ì (í) ìí 6:42, Baoquan He <bhe@xxxxxxxxxx>ëì ìì:
>
> On 06/13/20 at 11:51am, Jaewon Kim wrote:
> > zone_watermark_fast was introduced by commit 48ee5f3696f6 ("mm,
> > page_alloc: shortcut watermark checks for order-0 pages"). The commit
> > simply checks if free pages is bigger than watermark without additional
> > calculation such like reducing watermark.
> >
> > It considered free cma pages but it did not consider highatomic
> > reserved. This may incur exhaustion of free pages except high order
> > atomic free pages.
> >
> > Assume that reserved_highatomic pageblock is bigger than watermark min,
> > and there are only few free pages except high order atomic free. Because
> > zone_watermark_fast passes the allocation without considering high order
> > atomic free, normal reclaimable allocation like GFP_HIGHUSER will
> > consume all the free pages. Then finally order-0 atomic allocation may
> > fail on allocation.
> >
> > This means watermark min is not protected against non-atomic allocation.
> > The order-0 atomic allocation with ALLOC_HARDER unwantedly can be
> > failed. Additionally the __GFP_MEMALLOC allocation with
> > ALLOC_NO_WATERMARKS also can be failed.
> >
> > To avoid the problem, zone_watermark_fast should consider highatomic
> > reserve. If the actual size of high atomic free is counted accurately
> > like cma free, we may use it. On this patch just use
> > nr_reserved_highatomic. Additionally introduce
> > __zone_watermark_unusable_free to factor out common parts between
> > zone_watermark_fast and __zone_watermark_ok.
> >
> > This is trace log which shows GFP_HIGHUSER consumes free pages right
> > before ALLOC_NO_WATERMARKS.
> >
> > <...>-22275 [006] .... 889.213383: mm_page_alloc: page=00000000d2be5665 pfn=970744 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > <...>-22275 [006] .... 889.213385: mm_page_alloc: page=000000004b2335c2 pfn=970745 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > <...>-22275 [006] .... 889.213387: mm_page_alloc: page=00000000017272e1 pfn=970278 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > <...>-22275 [006] .... 889.213389: mm_page_alloc: page=00000000c4be79fb pfn=970279 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > <...>-22275 [006] .... 889.213391: mm_page_alloc: page=00000000f8a51d4f pfn=970260 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > <...>-22275 [006] .... 889.213393: mm_page_alloc: page=000000006ba8f5ac pfn=970261 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > <...>-22275 [006] .... 889.213395: mm_page_alloc: page=00000000819f1cd3 pfn=970196 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > <...>-22275 [006] .... 889.213396: mm_page_alloc: page=00000000f6b72a64 pfn=970197 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
> > kswapd0-1207 [005] ...1 889.213398: mm_page_alloc: page= (null) pfn=0 order=0 migratetype=1 nr_free=3650 gfp_flags=GFP_NOWAIT|__GFP_HIGHMEM|__GFP_NOWARN|__GFP_MOVABLE
> >
> > This is an example of ALLOC_HARDER allocation failure.
> >
> > <4>[ 6207.637280] [3: Binder:9343_3:22875] Binder:9343_3: page allocation failure: order:0, mode:0x480020(GFP_ATOMIC), nodemask=(null)
> > <4>[ 6207.637311] [3: Binder:9343_3:22875] Call trace:
> > <4>[ 6207.637346] [3: Binder:9343_3:22875] [<ffffff8008f40f8c>] dump_stack+0xb8/0xf0
> > <4>[ 6207.637356] [3: Binder:9343_3:22875] [<ffffff8008223320>] warn_alloc+0xd8/0x12c
> > <4>[ 6207.637365] [3: Binder:9343_3:22875] [<ffffff80082245e4>] __alloc_pages_nodemask+0x120c/0x1250
> > <4>[ 6207.637374] [3: Binder:9343_3:22875] [<ffffff800827f6e8>] new_slab+0x128/0x604
> > <4>[ 6207.637381] [3: Binder:9343_3:22875] [<ffffff800827b0cc>] ___slab_alloc+0x508/0x670
> > <4>[ 6207.637387] [3: Binder:9343_3:22875] [<ffffff800827ba00>] __kmalloc+0x2f8/0x310
> > <4>[ 6207.637396] [3: Binder:9343_3:22875] [<ffffff80084ac3e0>] context_struct_to_string+0x104/0x1cc
> > <4>[ 6207.637404] [3: Binder:9343_3:22875] [<ffffff80084ad8fc>] security_sid_to_context_core+0x74/0x144
> > <4>[ 6207.637412] [3: Binder:9343_3:22875] [<ffffff80084ad880>] security_sid_to_context+0x10/0x18
> > <4>[ 6207.637421] [3: Binder:9343_3:22875] [<ffffff800849bd80>] selinux_secid_to_secctx+0x20/0x28
> > <4>[ 6207.637430] [3: Binder:9343_3:22875] [<ffffff800849109c>] security_secid_to_secctx+0x3c/0x70
> > <4>[ 6207.637442] [3: Binder:9343_3:22875] [<ffffff8008bfe118>] binder_transaction+0xe68/0x454c
> > <4>[ 6207.637569] [3: Binder:9343_3:22875] Mem-Info:
> > <4>[ 6207.637595] [3: Binder:9343_3:22875] active_anon:102061 inactive_anon:81551 isolated_anon:0
> > <4>[ 6207.637595] [3: Binder:9343_3:22875] active_file:59102 inactive_file:68924 isolated_file:64
> > <4>[ 6207.637595] [3: Binder:9343_3:22875] unevictable:611 dirty:63 writeback:0 unstable:0
> > <4>[ 6207.637595] [3: Binder:9343_3:22875] slab_reclaimable:13324 slab_unreclaimable:44354
> > <4>[ 6207.637595] [3: Binder:9343_3:22875] mapped:83015 shmem:4858 pagetables:26316 bounce:0
> > <4>[ 6207.637595] [3: Binder:9343_3:22875] free:2727 free_pcp:1035 free_cma:178
> > <4>[ 6207.637616] [3: Binder:9343_3:22875] Node 0 active_anon:408244kB inactive_anon:326204kB active_file:236408kB inactive_file:275696kB unevictable:2444kB isolated(anon):0kB isolated(file):256kB mapped:332060kB dirty:252kB writeback:0kB shmem:19432kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
> > <4>[ 6207.637627] [3: Binder:9343_3:22875] Normal free:10908kB min:6192kB low:44388kB high:47060kB active_anon:409160kB inactive_anon:325924kB active_file:235820kB inactive_file:276628kB unevictable:2444kB writepending:252kB present:3076096kB managed:2673676kB mlocked:2444kB kernel_stack:62512kB pagetables:105264kB bounce:0kB free_pcp:4140kB local_pcp:40kB free_cma:712kB
> > <4>[ 6207.637632] [3: Binder:9343_3:22875] lowmem_reserve[]: 0 0
> > <4>[ 6207.637637] [3: Binder:9343_3:22875] Normal: 505*4kB (H) 357*8kB (H) 201*16kB (H) 65*32kB (H) 1*64kB (H) 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 10236kB
> > <4>[ 6207.637655] [3: Binder:9343_3:22875] 138826 total pagecache pages
> > <4>[ 6207.637663] [3: Binder:9343_3:22875] 5460 pages in swap cache
> > <4>[ 6207.637668] [3: Binder:9343_3:22875] Swap cache stats: add 8273090, delete 8267506, find 1004381/4060142
> >
> > This is an example of ALLOC_NO_WATERMARKS allocation failure.
> >
> > <6>[ 156.701551] [4: kswapd0: 1209] kswapd0 cpuset=/ mems_allowed=0
> > <4>[ 156.701563] [4: kswapd0: 1209] CPU: 4 PID: 1209 Comm: kswapd0 Tainted: G W 4.14.113-18113966 #1
> > <4>[ 156.701572] [4: kswapd0: 1209] Call trace:
> > <4>[ 156.701605] [4: kswapd0: 1209] [<0000000000000000>] dump_stack+0x68/0x90
> > <4>[ 156.701612] [4: kswapd0: 1209] [<0000000000000000>] warn_alloc+0x104/0x198
> > <4>[ 156.701617] [4: kswapd0: 1209] [<0000000000000000>] __alloc_pages_nodemask+0xdc0/0xdf0
> > <4>[ 156.701623] [4: kswapd0: 1209] [<0000000000000000>] zs_malloc+0x148/0x3d0
> > <4>[ 156.701630] [4: kswapd0: 1209] [<0000000000000000>] zram_bvec_rw+0x250/0x568
> > <4>[ 156.701634] [4: kswapd0: 1209] [<0000000000000000>] zram_rw_page+0x8c/0xe0
> > <4>[ 156.701640] [4: kswapd0: 1209] [<0000000000000000>] bdev_write_page+0x70/0xbc
> > <4>[ 156.701645] [4: kswapd0: 1209] [<0000000000000000>] __swap_writepage+0x58/0x37c
> > <4>[ 156.701649] [4: kswapd0: 1209] [<0000000000000000>] swap_writepage+0x40/0x4c
> > <4>[ 156.701654] [4: kswapd0: 1209] [<0000000000000000>] shrink_page_list+0xc3c/0xf54
> > <4>[ 156.701659] [4: kswapd0: 1209] [<0000000000000000>] shrink_inactive_list+0x2b0/0x61c
> > <4>[ 156.701664] [4: kswapd0: 1209] [<0000000000000000>] shrink_node_memcg+0x23c/0x618
> > <4>[ 156.701668] [4: kswapd0: 1209] [<0000000000000000>] shrink_node+0x1c8/0x304
> > <4>[ 156.701673] [4: kswapd0: 1209] [<0000000000000000>] kswapd+0x680/0x7c4
> > <4>[ 156.701679] [4: kswapd0: 1209] [<0000000000000000>] kthread+0x110/0x120
> > <4>[ 156.701684] [4: kswapd0: 1209] [<0000000000000000>] ret_from_fork+0x10/0x18
> > <4>[ 156.701689] [4: kswapd0: 1209] Mem-Info:
> > <4>[ 156.701712] [4: kswapd0: 1209] active_anon:88690 inactive_anon:88630 isolated_anon:0
> > <4>[ 156.701712] [4: kswapd0: 1209] active_file:99173 inactive_file:169305 isolated_file:32
> > <4>[ 156.701712] [4: kswapd0: 1209] unevictable:48292 dirty:538 writeback:38 unstable:0
> > <4>[ 156.701712] [4: kswapd0: 1209] slab_reclaimable:15131 slab_unreclaimable:47762
> > <4>[ 156.701712] [4: kswapd0: 1209] mapped:274654 shmem:2824 pagetables:25088 bounce:0
> > <4>[ 156.701712] [4: kswapd0: 1209] free:2489 free_pcp:444 free_cma:3
> > <4>[ 156.701728] [4: kswapd0: 1209] Node 0 active_anon:354760kB inactive_anon:354520kB active_file:396692kB inactive_file:677220kB unevictable:193168kB isolated(anon):0kB isolated(file):128kB mapped:1098616kB dirty:2152kB writeback:152kB shmem:11296kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
> > <4>[ 156.701738] [4: kswapd0: 1209] Normal free:9956kB min:7428kB low:93440kB high:97032kB active_anon:355176kB inactive_anon:354580kB active_file:396196kB inactive_file:677284kB unevictable:193168kB writepending:2304kB present:4081664kB managed:3593324kB mlocked:193168kB kernel_stack:55008kB pagetables:100352kB bounce:0kB free_pcp:1776kB local_pcp:656kB free_cma:12kB
> > <4>[ 156.701741] [4: kswapd0: 1209] lowmem_reserve[]: 0 0
> > <4>[ 156.701747] [4: kswapd0: 1209] Normal: 196*4kB (H) 141*8kB (H) 109*16kB (H) 63*32kB (H) 20*64kB (H) 8*128kB (H) 2*256kB (H) 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 9000kB
> >
> > Reported-by: Yong-Taek Lee <ytk.lee@xxxxxxxxxxx>
> > Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
> > Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
> > ---
> > v2: factor out common part
> > v1: consider highatomic reserve
> > ---
> > mm/page_alloc.c | 61 ++++++++++++++++++++++++++++---------------------
> > 1 file changed, 35 insertions(+), 26 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 48eb0f1410d4..c2177e056f19 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3487,6 +3487,29 @@ static noinline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
> > }
> > ALLOW_ERROR_INJECTION(should_fail_alloc_page, TRUE);
> >
> > +static inline long __zone_watermark_unusable_free(struct zone *z,
> > + unsigned int order, unsigned int alloc_flags)
> > +{
> > + const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
> > + long unusable_free = (1 << order) - 1;
> > +
> > + /*
> > + * If the caller does not have rights to ALLOC_HARDER then subtract
> > + * the high-atomic reserves. This will over-estimate the size of the
> > + * atomic reserve but it avoids a search.
> > + */
> > + if (likely(!alloc_harder))
> > + unusable_free += z->nr_reserved_highatomic;
> > +
> > +#ifdef CONFIG_CMA
> > + /* If allocation can't use CMA areas don't use free CMA pages */
> > + if (!(alloc_flags & ALLOC_CMA))
> > + unusable_free += zone_page_state(z, NR_FREE_CMA_PAGES);
> > +#endif
> > +
> > + return unusable_free;
> > +}
> > +
> > /*
> > * Return true if free base pages are above 'mark'. For high-order checks it
> > * will return true of the order-0 watermark is reached and there is at least
> > @@ -3502,19 +3525,12 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
> > const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
> >
> > /* free_pages may go negative - that's OK */
> > - free_pages -= (1 << order) - 1;
> > + free_pages -= __zone_watermark_unusable_free(z, order, alloc_flags);
> >
> > if (alloc_flags & ALLOC_HIGH)
> > min -= min / 2;
> >
> > - /*
> > - * If the caller does not have rights to ALLOC_HARDER then subtract
> > - * the high-atomic reserves. This will over-estimate the size of the
> > - * atomic reserve but it avoids a search.
> > - */
> > - if (likely(!alloc_harder)) {
> > - free_pages -= z->nr_reserved_highatomic;
> > - } else {
> > + if (unlikely(alloc_harder)) {
> > /*
> > * OOM victims can try even harder than normal ALLOC_HARDER
> > * users on the grounds that it's definitely going to be in
> > @@ -3527,13 +3543,6 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
> > min -= min / 4;
> > }
> >
> > -
> > -#ifdef CONFIG_CMA
> > - /* If allocation can't use CMA areas don't use free CMA pages */
> > - if (!(alloc_flags & ALLOC_CMA))
> > - free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
> > -#endif
> > -
> > /*
> > * Check watermarks for an order-0 allocation request. If these
> > * are not met, then a high-order request also cannot go ahead
> > @@ -3582,14 +3591,11 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
> > unsigned long mark, int highest_zoneidx,
> > unsigned int alloc_flags)
> > {
> > - long free_pages = zone_page_state(z, NR_FREE_PAGES);
> > - long cma_pages = 0;
> > + long free_pages;
> > + long unusable_free;
> >
> > -#ifdef CONFIG_CMA
> > - /* If allocation can't use CMA areas don't use free CMA pages */
> > - if (!(alloc_flags & ALLOC_CMA))
> > - cma_pages = zone_page_state(z, NR_FREE_CMA_PAGES);
> > -#endif
> > + free_pages = zone_page_state(z, NR_FREE_PAGES);
> > + unusable_free = __zone_watermark_unusable_free(z, order, alloc_flags);
> >
> > /*
> > * Fast check for order-0 only. If this fails then the reserves
> > @@ -3598,9 +3604,12 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
> > * the caller is !atomic then it'll uselessly search the free
> > * list. That corner case is then slower but it is harmless.
>
> Do we need remove or adjust the code comment at this place? So Mel have
> foreseen the corner case, just reclaiming to unreserve the highatomic
> might be ignored.
>
Hello thank you for your comment.
My previous mail to Vlastimil Babka seems to have html.
Let me put again here because I also think the comment should be changed.
I'd like to hear opinions from the open source community.
Additionally actually I think we need accurate counting of highatomic
free after this patch.
----------------------------------------------------------------------------------------
As Mel also agreed with me in v1 mail thread, this highatomic reserved should
be considered even in watermark fast.
The comment, I think, may need to be changed. Prior to this patch, non
highatomic
allocation may do useless search, but it also can take ALL non highatomic free.
With this patch, non highatomic allocation will NOT do useless search. Rather,
it may be required direct reclamation even when there are some non
high atomic free.
i.e)
In following situation, watermark check fails (9MB - 8MB < 4MB) though there are
enough free (9MB - 4MB > 4MB). If this is really matter, we need to
count highatomic
free accurately.
min : 4MB,
highatomic reserved : 8MB
Total free : 9MB
actual highatomic free : 4MB
non highatomic free : 5MB
> > */
> > - if (!order && (free_pages - cma_pages) >
> > - mark + z->lowmem_reserve[highest_zoneidx])
> > - return true;
> > + if (!order) {
> > + long fast_free = free_pages - unusable_free;
> > +
> > + if (fast_free > mark + z->lowmem_reserve[highest_zoneidx])
> > + return true;
> > + }
> >
> > return __zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags,
> > free_pages);
> > --
> > 2.17.1
> >
> >
>