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SubjectRe: [PATCH] mm/shmem: Do not wait for lock_page() in shmem_unused_huge_shrink()
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f2fs is doing

page = f2fs_pagecache_get_page(inode->i_mapping, 0, FGP_LOCK|FGP_NOWAIT, 0);

which calls

struct page *pagecache_get_page(inode->i_mapping, 0, FGP_LOCK|FGP_NOWAIT, 0);

. Then, can't we define

static inline struct page *find_trylock_page(struct address_space *mapping,
pgoff_t offset)
{
return pagecache_get_page(mapping, offset, FGP_LOCK|FGP_NOWAIT, 0);
}

and replace find_lock_page() with find_trylock_page() ?

Also, won't

----------
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 34ce3ebf..0cfc329 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -479,6 +479,8 @@ static inline int trylock_page(struct page *page)
static inline void lock_page(struct page *page)
{
might_sleep();
+ WARN_ONCE(current->flags & PF_MEMALLOC,
+ "lock_page() from reclaim context might deadlock");
if (!trylock_page(page))
__lock_page(page);
}
@@ -491,6 +493,8 @@ static inline void lock_page(struct page *page)
static inline int lock_page_killable(struct page *page)
{
might_sleep();
+ WARN_ONCE(current->flags & PF_MEMALLOC,
+ "lock_page_killable() from reclaim context might deadlock");
if (!trylock_page(page))
return __lock_page_killable(page);
return 0;
----------
help find lock_page() users in deep reclaim paths?

----------
[ 100.314083] ------------[ cut here ]------------
[ 100.315695] lock_page() from reclaim context might deadlock
[ 100.315708] WARNING: CPU: 1 PID: 56 at ./include/linux/pagemap.h:483 pagecache_get_page+0x245/0x250
[ 100.319686] Modules linked in: sg pcspkr i2c_piix4 vmw_vmci shpchp sd_mod ata_generic pata_acpi serio_raw vmwgfx drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm ahci mptspi libahci scsi_transport_spi mptscsih ata_piix mptbase i2c_core e1000 libata ipv6
[ 100.325951] CPU: 1 PID: 56 Comm: kswapd0 Kdump: loaded Not tainted 4.16.0-rc5-next-20180315+ #696
[ 100.328439] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
[ 100.331625] RIP: 0010:pagecache_get_page+0x245/0x250
[ 100.333211] RSP: 0018:ffffc9000085bc00 EFLAGS: 00010286
[ 100.334832] RAX: 0000000000000000 RBX: ffffea0004ad3100 RCX: 0000000000000007
[ 100.336900] RDX: 0000000000000b63 RSI: ffff88013aa0b700 RDI: ffff88013aa0ae80
[ 100.339068] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
[ 100.341108] R10: 0000000000000040 R11: 0000000000000000 R12: ffff880139b6e0c8
[ 100.343153] R13: 0000000000000000 R14: ffffffff82068220 R15: 0000000000000002
[ 100.345242] FS: 0000000000000000(0000) GS:ffff88013bc40000(0000) knlGS:0000000000000000
[ 100.347510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 100.349277] CR2: 00007f326c67e000 CR3: 000000000200f006 CR4: 00000000001606e0
[ 100.351343] Call Trace:
[ 100.352374] ? iput+0x52/0x2f0
[ 100.353567] shmem_unused_huge_shrink+0x2e9/0x380
[ 100.355112] super_cache_scan+0x17a/0x180
[ 100.356553] shrink_slab+0x218/0x590
[ 100.357854] shrink_node+0x346/0x350
[ 100.359161] kswapd+0x322/0x930
[ 100.360370] kthread+0xf0/0x130
[ 100.361566] ? mem_cgroup_shrink_node+0x320/0x320
[ 100.363112] ? kthread_create_on_node+0x60/0x60
[ 100.364634] ret_from_fork+0x3a/0x50
[ 100.365943] Code: db e8 70 4c 01 00 e9 5e fe ff ff 80 3d 44 51 f8 00 00 0f 85 46 ff ff ff 48 c7 c7 60 11 df 81 c6 05 30 51 f8 00 01 e8 5b 86 ee ff <0f> 0b e9 2c ff ff ff 0f 1f 40 00 83 e2 02 53 8b 8f 48 01 00 00
[ 100.371197] ---[ end trace b50eee6f891efec3 ]---
----------
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