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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1wIQc7-00000007Dpy-0PSw; Thu, 30 Apr 2026 12:35:31 +0000 Date: Thu, 30 Apr 2026 13:35:30 +0100 From: Matthew Wilcox To: "Barry Song (Xiaomi)" Cc: akpm@linux-foundation.org, linux-mm@kvack.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jack@suse.cz, pfalcato@suse.de, wanglian@kylinos.cn, chentao@kylinos.cn, lianux.mm@gmail.com, kunwu.chan@gmail.com, liyangouwen1@oppo.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org Subject: Re: [PATCH v2 4/5] mm: Don't retry page fault if folio is uptodate during swap-in Message-ID: References: <20260430040427.4672-1-baohua@kernel.org> <20260430040427.4672-5-baohua@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260430040427.4672-5-baohua@kernel.org> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9D04BC000E X-Stat-Signature: 1yfgyfm6jjfywb8ok7c9p9fq5ccwypy9 X-Rspam-User: X-HE-Tag: 1777552544-411663 X-HE-Meta: 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 00ftp8jE 3Rl/N7pp/vwCw9VSw0aHEL9Gk0yPNNuzUMRoNnv86/PBDWET89CWGdx6/79f9l8IXQXQDa6XBDEae20rjjWv0TE++fw1/+mcbf0qQQq5Y1tbToSdIGmg9kVaikzMJpA7Pd/qJkMnPe/1diBEWPb3liXQRjlQjsZCcpxDF+KNQHxSyYX6MAFWe2xaDKjSufXtUUimES68h5PNbyBO2+ergLiAOI2U0K83MTUw1PYex1pvPX9lGXdoz7pI2VhSAwpbCy1HNi5I1lVrs7bEHMBsLSiyeVa+5avYPVosIxZt+Tb0sNcctyTL7PcoCRGgqan+GaSZgLYHNNoDQKEDmqVCyv0euxhbbstvPvh6G3OI4TmivXMnipRtu6pDYTg/dlsK0AD6v Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 30, 2026 at 12:04:26PM +0800, Barry Song (Xiaomi) wrote: > If we are waiting for long I/O to complete, it makes sense to > avoid holding locks for too long. However, if the folio is > uptodate, we are likely only waiting for a concurrent PTE > update to finish. Retrying the entire page fault seems > excessive. I think the idea is good, but the implementation is misplaced. The check for folio_uptodate() should be inside folio_lock_or_retry() rather than tampering with FAULT_FLAG_ALLOW_RETRY in its caller. Similarly for your next patch. > Signed-off-by: Barry Song (Xiaomi) > --- > mm/memory.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index 0c740ca363cc..a2e4f2d87ec8 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4949,6 +4949,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > } > > swapcache = folio; > + /* > + * If the folio is uptodate, we are likely only waiting for > + * another concurrent PTE mapping to complete, which should > + * be brief. No need to drop the lock and retry the fault. > + */ > + if (folio_test_uptodate(folio)) > + vmf->flags &= ~FAULT_FLAG_ALLOW_RETRY; > ret |= folio_lock_or_retry(folio, vmf); > if (ret & VM_FAULT_RETRY) { > if (fault_flag_allow_retry_first(vmf->flags) && > -- > 2.39.3 (Apple Git-146) > >