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Tue, 10 Jun 2025 05:07:29 -0700 (PDT) MIME-Version: 1.0 References: <20250609171751.36305-1-ryncsn@gmail.com> In-Reply-To: From: Kairui Song Date: Tue, 10 Jun 2025 20:07:11 +0800 X-Gm-Features: AX0GCFuWYIwav4rBaHsjrNi9kdwf54qgTpqYzrPnbbTLYKH9o3hXXphGU3Ij5ME Message-ID: Subject: Re: [PATCH v2] mm/shmem, swap: fix softlockup with mTHP swapin To: Nhat Pham Cc: linux-mm@kvack.org, Andrew Morton , Hugh Dickins , Baolin Wang , Kemeng Shi , Chris Li , Baoquan He , Barry Song , Usama Arif , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 91BB71C0008 X-Stat-Signature: dafksqbwny8yakf5xwej8u35ge878hha X-Rspam-User: X-HE-Tag: 1749557251-378166 X-HE-Meta: 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 5HiotUms s0Xj7RONp1gPCRDY//sIKgu7j7vgneydr4hah0lhb9gFa/KjieCm2UTAAnYpNoVEy0bnN2KC309CduBj3fUSy3wtfqgV9T73aBQiMz93l8r7t1YALxiRP6aF+yBcQiD5yfWG775EmBmm8yRqhByEkirrzOaSOUZLLhtXvSy56yDt5tx+kt7qLaYzr3EI//xSHG/78Mj/zjOKWDZUaui+/51tFSCLzroe7+QSsHhZygx+HbD5eEiZBivB+D4GBOlV29FFnpj3PjRHapM9W++RhJKjmfCNw7LfYMdPLOpXhSnFohAIcKfP2fSGo6fkpokakBXTFFhV9n82AXApktDpC8LjD3zjds4/H9xqWdDmwe0U5AyTbhFVSbvzifJGasJaiDIU9aSL/w8R1gdM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 10, 2025 at 2:16=E2=80=AFAM Nhat Pham wrote= : > > On Mon, Jun 9, 2025 at 10:18=E2=80=AFAM Kairui Song wr= ote: > > > > From: Kairui Song > > > > Following softlockup can be easily reproduced on my test machine with: > > > > echo always > /sys/kernel/mm/transparent_hugepage/hugepages-64kB/enable= d > > swapon /dev/zram0 # zram0 is a 48G swap device > > mkdir -p /sys/fs/cgroup/memory/test > > echo 1G > /sys/fs/cgroup/test/memory.max > > echo $BASHPID > /sys/fs/cgroup/test/cgroup.procs > > while true; do > > dd if=3D/dev/zero of=3D/tmp/test.img bs=3D1M count=3D5120 > > cat /tmp/test.img > /dev/null > > rm /tmp/test.img > > done > > > > Then after a while: > > watchdog: BUG: soft lockup - CPU#0 stuck for 763s! [cat:5787] > > Modules linked in: zram virtiofs > > CPU: 0 UID: 0 PID: 5787 Comm: cat Kdump: loaded Tainted: G = L 6.15.0.orig-gf3021d9246bc-dirty #118 PREEMPT(voluntary)=C2=B7 > > Tainted: [L]=3DSOFTLOCKUP > > Hardware name: Red Hat KVM/RHEL-AV, BIOS 0.0.0 02/06/2015 > > RIP: 0010:mpol_shared_policy_lookup+0xd/0x70 > > Code: e9 b8 b4 ff ff 31 c0 c3 cc cc cc cc 90 90 90 90 90 90 90 90 90 90= 90 90 90 90 90 90 90 66 0f 1f 00 0f 1f 44 00 00 41 54 55 53 <48> 8b 1f 48 = 85 db 74 41 4c 8d 67 08 48 89 fb 48 89 f5 4c 89 e7 e8 > > RSP: 0018:ffffc90002b1fc28 EFLAGS: 00000202 > > RAX: 00000000001c20ca RBX: 0000000000724e1e RCX: 0000000000000001 > > RDX: ffff888118e214c8 RSI: 0000000000057d42 RDI: ffff888118e21518 > > RBP: 000000000002bec8 R08: 0000000000000001 R09: 0000000000000000 > > R10: 0000000000000bf4 R11: 0000000000000000 R12: 0000000000000001 > > R13: 00000000001c20ca R14: 00000000001c20ca R15: 0000000000000000 > > FS: 00007f03f995c740(0000) GS:ffff88a07ad9a000(0000) knlGS:00000000000= 00000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 00007f03f98f1000 CR3: 0000000144626004 CR4: 0000000000770eb0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > PKRU: 55555554 > > Call Trace: > > > > shmem_alloc_folio+0x31/0xc0 > > shmem_swapin_folio+0x309/0xcf0 > > ? filemap_get_entry+0x117/0x1e0 > > ? xas_load+0xd/0xb0 > > ? filemap_get_entry+0x101/0x1e0 > > shmem_get_folio_gfp+0x2ed/0x5b0 > > shmem_file_read_iter+0x7f/0x2e0 > > vfs_read+0x252/0x330 > > ksys_read+0x68/0xf0 > > do_syscall_64+0x4c/0x1c0 > > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > RIP: 0033:0x7f03f9a46991 > > Code: 00 48 8b 15 81 14 10 00 f7 d8 64 89 02 b8 ff ff ff ff eb bd e8 20= ad 01 00 f3 0f 1e fa 80 3d 35 97 10 00 00 74 13 31 c0 0f 05 <48> 3d 00 f0 = ff ff 77 4f c3 66 0f 1f 44 00 00 55 48 89 e5 48 83 ec > > RSP: 002b:00007fff3c52bd28 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > > RAX: ffffffffffffffda RBX: 0000000000040000 RCX: 00007f03f9a46991 > > RDX: 0000000000040000 RSI: 00007f03f98ba000 RDI: 0000000000000003 > > RBP: 00007fff3c52bd50 R08: 0000000000000000 R09: 00007f03f9b9a380 > > R10: 0000000000000022 R11: 0000000000000246 R12: 0000000000040000 > > R13: 00007f03f98ba000 R14: 0000000000000003 R15: 0000000000000000 > > > > > > The reason is simple, readahead brought some order 0 folio in swap > > cache, and the swapin mTHP folio being allocated is in confict with it, > > so swapcache_prepare fails and causes shmem_swap_alloc_folio to return > > -EEXIST, and shmem simply retries again and again causing this loop. > > > > Fix it by applying a similar fix for anon mTHP swapin. > > > > The performance change is very slight, time of swapin 10g zero folios > > with shmem (test for 12 times): > > Before: 2.47s > > After: 2.48s > > > > Fixes: 1dd44c0af4fa1 ("mm: shmem: skip swapcache for swapin of synchron= ous swap device") > > Signed-off-by: Kairui Song > > LGTM. > Acked-by: Nhat Pham > > > > > --- > > > > V1: https://lore.kernel.org/linux-mm/20250608192713.95875-1-ryncsn@gmai= l.com/ > > Updates: > > - Move non_swapcache_batch check before swapcache_prepare, I was > > expecting this could improve the performance, turns out it barely > > helps and may even cause more overhead in some cases. [ Barry Song ] > > - Remove zero map check, no need to do that for shmem [ Barry Song, > > Baolin Wang ] > > - Fix build bot error. > > > > mm/memory.c | 20 -------------------- > > mm/shmem.c | 4 +++- > > mm/swap.h | 23 +++++++++++++++++++++++ > > 3 files changed, 26 insertions(+), 21 deletions(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 9ead7ab07e8e..3845ed068d74 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -4313,26 +4313,6 @@ static struct folio *__alloc_swap_folio(struct v= m_fault *vmf) > > } > > > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > > -static inline int non_swapcache_batch(swp_entry_t entry, int max_nr) > > -{ > > - struct swap_info_struct *si =3D swp_swap_info(entry); > > - pgoff_t offset =3D swp_offset(entry); > > - int i; > > - > > - /* > > - * While allocating a large folio and doing swap_read_folio, wh= ich is > > - * the case the being faulted pte doesn't have swapcache. We ne= ed to > > - * ensure all PTEs have no cache as well, otherwise, we might g= o to > > - * swap devices while the content is in swapcache. > > - */ > > - for (i =3D 0; i < max_nr; i++) { > > - if ((si->swap_map[offset + i] & SWAP_HAS_CACHE)) > > - return i; > > - } > > - > > - return i; > > -} > > - > > /* > > * Check if the PTEs within a range are contiguous swap entries > > * and have consistent swapcache, zeromap. > > diff --git a/mm/shmem.c b/mm/shmem.c > > index 73182e904f9c..a4fdfbd086f1 100644 > > --- a/mm/shmem.c > > +++ b/mm/shmem.c > > @@ -2256,6 +2256,7 @@ static int shmem_swapin_folio(struct inode *inode= , pgoff_t index, > > folio =3D swap_cache_get_folio(swap, NULL, 0); > > order =3D xa_get_order(&mapping->i_pages, index); > > if (!folio) { > > + int nr_pages =3D 1 << order; > > bool fallback_order0 =3D false; > > > > /* Or update major stats only when swapin succeeds?? */ > > @@ -2271,7 +2272,8 @@ static int shmem_swapin_folio(struct inode *inode= , pgoff_t index, > > * to swapin order-0 folio, as well as for zswap case. > > nit: maybe update the above comment? Good idea. There are already some comments in non_swapcache_batch and I've updated it for this commit, but mentioning it here definitely helps more. > > > */ > > if (order > 0 && ((vma && unlikely(userfaultfd_armed(vm= a))) || > > - !zswap_never_enabled())) > > + !zswap_never_enabled() || > > + non_swapcache_batch(swap, nr_pages) != =3D nr_pages)) > > fallback_order0 =3D true; > > > > /* Skip swapcache for synchronous device. */ > > diff --git a/mm/swap.h b/mm/swap.h > > index e87a0f19a0ee..911ad5ff0f89 100644 > > --- a/mm/swap.h > > +++ b/mm/swap.h > > @@ -108,6 +108,25 @@ static inline int swap_zeromap_batch(swp_entry_t e= ntry, int max_nr, > > return find_next_bit(sis->zeromap, end, start) - start; > > } > > >