Re: [PATCH v3] page_alloc: consider highatomic reserve in wmartermark fast

From: Jaewon Kim
Date: Tue Jun 16 2020 - 10:10:32 EST

2020ë 6ì 16ì (í) ìí 7:21, Vlastimil Babka <vbabka@xxxxxxx>ëì ìì:
>
> On 6/17/20 4:05 AM, Jaewon Kim wrote:
>
> Please fix typo "wmartermark" in subject.
Oops
Let me fix typo in next version as watermark
>
> > 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 an example of ALLOC_HARDER allocation failure using v4.19 based
> > kernel.
> >
> > <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
>
> These are better to read after removing the timestamp and process info part,
> i.e. "<4>[ 6207.637668] [3: Binder:9343_3:22875]" (also in the other examples
> below).
>
Good comment
Let me remove those timestamp and process info.
> > This is an example of ALLOC_NO_WATERMARKS allocation failure using v4.14
> > based kernel.
> >
> > [ 4738.329298] kswapd0: page allocation failure: order:0, mode:0x140000a(GFP_NOIO|__GFP_HIGHMEM|__GFP_MOVABLE), nodemask=(null)
> > [ 4738.329325] kswapd0 cpuset=/ mems_allowed=0
> > [ 4738.329339] CPU: 4 PID: 1221 Comm: kswapd0 Not tainted 4.14.113-18770262-userdebug #1
> > [ 4738.329350] Call trace:
> > [ 4738.329366] [<0000000000000000>] dump_backtrace+0x0/0x248
> > [ 4738.329377] [<0000000000000000>] show_stack+0x18/0x20
> > [ 4738.329390] [<0000000000000000>] __dump_stack+0x20/0x28
> > [ 4738.329398] [<0000000000000000>] dump_stack+0x68/0x90
> > [ 4738.329409] [<0000000000000000>] warn_alloc+0x104/0x198
> > [ 4738.329417] [<0000000000000000>] __alloc_pages_nodemask+0xdc0/0xdf0
> > [ 4738.329427] [<0000000000000000>] zs_malloc+0x148/0x3d0
> > [ 4738.329438] [<0000000000000000>] zram_bvec_rw+0x410/0x798
> > [ 4738.329446] [<0000000000000000>] zram_rw_page+0x88/0xdc
> > [ 4738.329455] [<0000000000000000>] bdev_write_page+0x70/0xbc
> > [ 4738.329463] [<0000000000000000>] __swap_writepage+0x58/0x37c
> > [ 4738.329469] [<0000000000000000>] swap_writepage+0x40/0x4c
> > [ 4738.329478] [<0000000000000000>] shrink_page_list+0xc30/0xf48
> > [ 4738.329486] [<0000000000000000>] shrink_inactive_list+0x2b0/0x61c
> > [ 4738.329494] [<0000000000000000>] shrink_node_memcg+0x23c/0x618
> > [ 4738.329501] [<0000000000000000>] shrink_node+0x1c8/0x304
> > [ 4738.329509] [<0000000000000000>] kswapd+0x680/0x7c4
> > [ 4738.329518] [<0000000000000000>] kthread+0x110/0x120
> > [ 4738.329527] [<0000000000000000>] ret_from_fork+0x10/0x18
> > [ 4738.329538] Mem-Info:
> > [ 4738.329574] active_anon:111826 inactive_anon:65557 isolated_anon:0\x0a active_file:44260 inactive_file:83422 isolated_file:0\x0a unevictable:4158 dirty:117 writeback:0 unstable:0\x0a slab_reclaimable:13943 slab_unreclaimable:43315\x0a mapped:102511 shmem:3299 pagetables:19566 bounce:0\x0a free:3510 free_pcp:553 free_cma:0
> > [ 4738.329593] Node 0 active_anon:447304kB inactive_anon:262228kB active_file:177040kB inactive_file:333688kB unevictable:16632kB isolated(anon):0kB isolated(file):0kB mapped:410044kB d irty:468kB writeback:0kB shmem:13196kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
> > [ 4738.329603] Normal free:14040kB min:7440kB low:94500kB high:98136kB reserved_highatomic:32768KB active_anon:447336kB inactive_anon:261668kB active_file:177572kB inactive_file:333768k B unevictable:16632kB writepending:480kB present:4081664kB managed:3637088kB mlocked:16632kB kernel_stack:47072kB pagetables:78264kB bounce:0kB free_pcp:2280kB local_pcp:720kB free_cma:0kB [ 4738.329607] lowmem_reserve[]: 0 0
> > [ 4738.329615] Normal: 860*4kB (H) 453*8kB (H) 180*16kB (H) 26*32kB (H) 34*64kB (H) 6*128kB (H) 2*256kB (H) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 14232kB
> >
> > 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
> >
> > Reported-by: Yong-Taek Lee <ytk.lee@xxxxxxxxxxx>
> > Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
> > Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Thank you for the Acked-by, let me add your Acked-by in next version.
>
> > ---
> > v3: change log in description to one having reserved_highatomic
> > change comment in code
> > v2: factor out common part
> > v1: consider highatomic reserve
> > ---
> > mm/page_alloc.c | 66 +++++++++++++++++++++++++++----------------------
> > 1 file changed, 36 insertions(+), 30 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 48eb0f1410d4..fe83f88ce188 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
> > @@ -3582,25 +3591,22 @@ 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
> > - * need to be calculated. There is a corner case where the check
> > - * passes but only the high-order atomic reserve are free. If
> > - * the caller is !atomic then it'll uselessly search the free
> > - * list. That corner case is then slower but it is harmless.
> > + * need to be calculated.
> > */
> > - 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);
> >
>