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Received: from 30.74.144.149(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XCJIB-._1791429397 cluster:ay36) by smtp.aliyun-inc.com; Thu, 08 Oct 2026 11:16:38 +0800 Message-ID: Date: Thu, 8 Oct 2026 11:16:36 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Make swapoff interruptible when unusing mms/shmem To: Chris Down , Andrew Morton Cc: Hugh Dickins , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Ying Huang , Kelley Nielsen , Vineeth Pillai , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2760C40009 X-Stat-Signature: zmo8wjmiq3nzqkuro99he9bqq9ry3kw6 X-HE-Tag: 1791429402-750624 X-HE-Meta: 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 conyk0wb wqrYBH5vR6UFtbfAVOyiXksZJ25c9Y7fbZvu/9RkBpz16RjiSkc2lbvUXaCchB1cJZvuRamCrKTWEDNY58PotTkMUJeDmRGVbyBEgtOG6jqXVOkI2w+K2FL7IlMvoztWA/uYpjyoDcdwiyiqUSJGn6ew9z2UF822aF2zjVnaMJeS6gBsIYyQtpWgTx+z/dqORPXfjh/ulC8lyplFpT2d4t2PGByDRCvdm2RRBQf/k2w1soHYuY4bp/JqbQPFz2p0AScsAfRqvkgTqcWnMHxcIGffpEkUXDG5/Y+2A4SgL7YyeFEoNIdmHvYixrJq51kbb39ePdC5FTrdSXhmtEVipLRV8Gtgc2NTO4TuhWiGonSl3JqXE7ezzdYYVAZq45smAZ0SbH4ju68/8iN5icHAZioCCxMZi9ICCDt/WvOgFf0mZpPiPyCkFJlDxtA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/1/26 7:17 AM, Chris Down wrote: > try_to_unuse() only checks for a pending signal between mms, and > shmem_unuse() doesn't check at all. That means that once swapoff gets to > a process or a shmem file with a lot swapped out, nothing can interrupt > it until every last page of it has been read back in. > > Just as one example of where this can concretely show up, freezing tasks > for suspend or hibernation has to wait for swapoff to notice the > freezer's fake signal, and gives up after freeze_timeout_msecs (20 > seconds by default). > > Here's a facetious example where one swaps out 2GiB of one process to a > swap file on ext4, starts swapoff, and half a second later tries to > freeze with pm_test=freezer. Writing to /sys/power/state then fails with > EBUSY and this in dmesg: > > Freezing user space processes failed after 20.003 seconds (1 tasks refusing to freeze, wq_busy=0): > task:swapoff state:D stack:0 pid:3175 tgid:3175 ppid:2955 task_flags:0x400100 flags:0x00000419 > Call trace: > [...] > io_schedule+0x44/0x70 > folio_wait_bit_common+0x1ec/0x3d0 > __folio_lock+0x24/0x40 > unuse_pte_range+0x2d0/0x348 > unuse_vma+0x158/0x248 > unuse_mm+0xfc/0x150 > try_to_unuse+0x104/0x3f8 > __do_sys_swapoff+0x220/0x5d8 > [...] > > The same goes for anything else that wants swapoff to stop, like an > admin hitting ^C in a panic, of course. > > Prior to commit b56a2d8af914 ("mm: rid swapoff of quadratic complexity") > try_to_unuse() was driven by find_next_to_unuse() which checks for a > signal before every entry, so let's restore that behaviour. > > Just as an example of the improvements, here's how long freezing takes > in the same test while swapoff is happening on my computer: > > before after > 400MiB anon 8.925s 0.028s > 400MiB shmem 1.639s 0.003s > 2GiB anon failed after 20.003s 0.011s > > Fixes: b56a2d8af914 ("mm: rid swapoff of quadratic complexity") > Signed-off-by: Chris Down > --- Make sense to me. But ... > mm/shmem.c | 4 ++++ > mm/swapfile.c | 2 ++ > 2 files changed, 6 insertions(+) > > diff --git a/mm/shmem.c b/mm/shmem.c > index ae08cff4500c..72c8a61db76f 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1742,6 +1742,10 @@ static int shmem_unuse_inode(struct inode *inode, unsigned int type) > if (ret < 0) > break; > > + if (signal_pending(current)) { > + ret = -EINTR; > + break; > + } > start = indices[folio_batch_count(&fbatch) - 1]; > } while (true); > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 254ce86fa923..c3288910b3e3 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -2689,6 +2689,8 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud, > pmd = pmd_offset(pud, addr); > do { > cond_resched(); > + if (signal_pending(current)) > + return -EINTR; Should we return -ERESTARTSYS instead based on the similar issue discussed in the following patch? https://lore.kernel.org/all/20260720044103.905191-1-richardycc@google.com/ > next = pmd_addr_end(addr, end); > ret = unuse_pte_range(vma, pmd, addr, next, type); > if (ret) > > base-commit: 2ddb90ee544ae97215afc4698dc223293997cc43