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From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 353761C000B X-Stat-Signature: zx156ojpunwg481t3nxbsipdfp56yhah X-HE-Tag: 1780365263-214410 X-HE-Meta: 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 3BKShRM0 cm6TrA+TuE6zLQcAmoAo23N/5Rt+JCS5ivF8ToqGlY5zgBUCyeVNtt1HNPS9kGCoBmtRtiBDhj1QfKSgpVSE+zp+c3MThx+vNCig4+ODJvIsRUk/t8j2t+FqAVQocaIdElhMgc48riWibVnxjkbKMIOx9Ad4BuLq+26tFLynsaIKao7FLuthw/9XxzPFsmD/qhWfUkZAqJ8UIoqE2M1CwEbQ96Vdo2CpHvSZ0mz0ObbIy4veNMqcEz3WOq1d/y/3YcwVY1aMzkroyT1nQ5qXk5570ZOi8beLK8dc9Rpcy9NFn+yZHlKl0JQm1nQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/6/2 01:08, Lorenzo Stoakes wrote: > On Mon, Jun 01, 2026 at 05:58:08PM +0200, Alexander Gordeev wrote: >> On Fri, May 22, 2026 at 01:47:24PM -0700, Andrew Morton wrote: >> >> Hi Andrew et al, >> >>> On Fri, 22 May 2026 08:59:55 -0600 Nico Pache wrote: >>> >>>> The following series provides khugepaged with the capability to collapse >>>> anonymous memory regions to mTHPs. >>> >>> Thanks, I've update mm.git's mm-unstable branch to this version. >>> >>> It sounds like I might be dropping it soon, haven't started looking at >>> that yet. But let's at least eyeball the latest version at this time. >>> >>> Sashiko was able to apply this, so the base-it-on-hotfixes thing worked >>> well, thanks. The AI checking made a few allegations: >> >> This series appears to cause hangs on s390 in linux-next. >> The issue is not easily reproducible, so it is not yet confirmed. >> Any ideas for a reliable reproducer that exercises the code path below? >> >> [ 2749.385719] sysrq: Show Blocked State >> [ 2749.385730] task:khugepaged state:D stack:0 pid:209 tgid:209 ppid:2 task_flags:0x200040 flags:0x00000000 >> [ 2749.385735] Call Trace: >> [ 2749.385736] [<0000017f63c8b226>] __schedule+0x316/0x890 >> [ 2749.385740] [<0000017f63c8b7dc>] schedule+0x3c/0xc0 >> [ 2749.385743] [<0000017f63c8b888>] schedule_preempt_disabled+0x28/0x40 >> [ 2749.385746] [<0000017f63c902ea>] rwsem_down_write_slowpath+0x2fa/0x8b0 >> [ 2749.385749] [<0000017f63c90910>] down_write+0x70/0x80 >> [ 2749.385752] [<0000017f6313407a>] collapse_huge_page+0x2ea/0x9e0 >> [ 2749.385755] [<0000017f6313491e>] mthp_collapse+0x1ae/0x1f0 >> [ 2749.385757] [<0000017f63134fda>] collapse_scan_pmd+0x67a/0x8f0 >> [ 2749.385760] [<0000017f6313751a>] collapse_single_pmd+0x15a/0x260 >> [ 2749.385762] [<0000017f6313792c>] collapse_scan_mm_slot.constprop.0+0x30c/0x470 >> [ 2749.385765] [<0000017f63137cb6>] khugepaged+0x226/0x240 >> [ 2749.385768] [<0000017f62db3128>] kthread+0x148/0x170 >> [ 2749.385770] [<0000017f62d2c238>] __ret_from_fork+0x48/0x220 >> [ 2749.385772] [<0000017f63c95d0a>] ret_from_fork+0xa/0x30 >> >> Thanks! > > Hi Alexander, > > Thanks for the report. > > It's a pity it's non-repro, I had Claude have a look at it and it couldn't find > a definite issue with the code at v18, all the locks seem balanced internally. > > Things it highlighted FWIW: > > - Far more mmap_write_lock()'s being taken - the stack-based approach calls > colapse_huge_page() multiple times per-PMD each of which entails an mmap read > lock/unlock and mmap write lock. > > - anon_vma write lock held for a much longer period over partial collapse. > > So maybe these are triggering issues rather than being the cause of them per-se? > > If you happen to see it again could you give the output for: > > 'echo t > /proc/sysrq-trigger' so we can track who holds the contended lock and > get more details on it? > > Also the .config would be useful. > > I'm guessing you've also not enabled mTHP in any way on the system? > > Repro-wise you could also: > > # echo 1 > /sys/kernel/mm/transparent_hugepage/khugepaged/scan_sleep_millisecs > # echo 1 > /sys/kernel/mm/transparent_hugepage/khugepaged/alloc_sleep_millisecs > > To get khugepaged going a more aggressively: > > $ for f in /sys/kernel/mm/transparent_hugepage/hugepages-*; do echo always | sudo tee $f/enabled; done > > Then maybe some stress-ng like sudo stress-ng --vm 4 --vm-bytes 2G --vm-method > all --timeout 5m (or maybe something more refined :)? > > Maybe some of this will help repro more reliably? > Cool! Maybe also worth trying with CONFIG_DETECT_HUNG_TASK=y and CONFIG_DETECT_HUNG_TASK_BLOCKER=y. # detect after 10s in D state instead of default 120s echo 10 > /proc/sys/kernel/hung_task_timeout_secs # optional: check more often; 0 means same as timeout echo 0 > /proc/sys/kernel/hung_task_check_interval_secs With that enabled, the kernel should hopefully tell us which task likely owns the rwsem. If it is writer-owned, I would expect that to be fairly reliable. Cheers, Lance