Hi Jaewon,
On Tue, Jun 09, 2020 at 06:51:28PM +0900, 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.
>
> 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
>
> Signed-off-by: Jaewon Kim <jaewon31....@samsung.com>
> Reported-by: Yong-Taek Lee <ytk....@samsung.com>
> ---
> mm/page_alloc.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 13cc653122b7..00869378d387 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3553,6 +3553,11 @@ static inline bool zone_watermark_fast(struct zone *z,
> unsigned int order,
> {
> long free_pages = zone_page_state(z, NR_FREE_PAGES);
> long cma_pages = 0;
> + long highatomic = 0;
> + const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
> +
> + if (likely(!alloc_harder))
> + highatomic = z->nr_reserved_highatomic;
>
> #ifdef CONFIG_CMA
> /* If allocation can't use CMA areas don't use free CMA pages */
> @@ -3567,8 +3572,12 @@ 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.
> */
> - if (!order && (free_pages - cma_pages) > mark +
> z->lowmem_reserve[classzone_idx])
> - return true;
> + if (!order) {
> + long fast_free = free_pages - cma_pages - highatomic;
With your change, it seems we share most code for getting free_pages
between zone_watermark_fast and __zone_watermark_ok. Only difference
between them is min calculation. If so, can we share most code between
them via introducing like __zone_watermark_free static inline function?
So, we didn't miss one place in future if we change something.
> +
> + if (fast_free > mark + z->lowmem_reserve[classzone_idx])
> + return true;
> + }
>
> return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
> free_pages);
> --
> 2.17.1
>
