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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id w10-20020a05690204ea00b00b7767ca747csm3435131ybs.25.2023.04.17.21.41.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Apr 2023 21:41:43 -0700 (PDT) Date: Mon, 17 Apr 2023 21:41:41 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Luis Chamberlain cc: hughd@google.com, akpm@linux-foundation.org, willy@infradead.org, brauner@kernel.org, linux-mm@kvack.org, p.raghav@samsung.com, da.gomez@samsung.com, a.manzanares@samsung.com, dave@stgolabs.net, yosryahmed@google.com, keescook@chromium.org, patches@lists.linux.dev, linux-kernel@vger.kernel.org, David Hildenbrand Subject: Re: [PATCH v2 4/6] shmem: skip page split if we're not reclaiming In-Reply-To: <20230309230545.2930737-5-mcgrof@kernel.org> Message-ID: References: <20230309230545.2930737-1-mcgrof@kernel.org> <20230309230545.2930737-5-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: ioyt4jz1jpf54ws5jpt4sija64853xdr X-Rspam-User: X-Rspamd-Queue-Id: BCD3080005 X-Rspamd-Server: rspam06 X-HE-Tag: 1681792904-93605 X-HE-Meta: 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 jlq2RMqX Ocde8vTpLsUSYHnpKeHo0i3kx1BCSt67G3Y+OoxUWiDXP1YQXLAWRAdtO+QGLRttm6hSrekzzvAGmTutlE3jABkEDYfcal3uEKPAQT099nGnHWDABzgyaEJTmBe8J9RLTzWh0cK1UrAIugPptmldmGFuA/dNUiPWMvPIEBvvVWjCjEU6fAvPwTHq0Pu4gP+eVyYEU9MU5oOdNP3gg7xFEbCeiurPLCGiQUw/AGbbBYJ/4kipMedaM9tPUfGi6+0RzPL6nABmvqQe7HbihjJBO9r0vTQOM3csXqKwb73ylfnFa3/wCKmtBB9eEQVw36pCswGNx6R/kggkegVZ2Meds517PlzBiqG7XDWvO8S45hlC0Cc4cr8MItG+NVPF5SEGdE0b9S06kptftcMSI/nJF/Jw6XOVG4t1ul05Of2xKZG1E1XvlUVX42glsexTbzpTa0+4L4XllPiOMIwY= 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: On Thu, 9 Mar 2023, Luis Chamberlain wrote: > In theory when info->flags & VM_LOCKED we should not be getting > shem_writepage() called so we should be verifying this with a > WARN_ON_ONCE(). Since we should not be swapping then best to ensure > we also don't do the folio split earlier too. So just move the check > early to avoid folio splits in case its a dubious call. > > We also have a similar early bail when !total_swap_pages so just move > that earlier to avoid the possible folio split in the same situation. > > Acked-by: David Hildenbrand > Reviewed-by: Christian Brauner > Signed-off-by: Luis Chamberlain > --- > mm/shmem.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 68e9970baf1e..dfd995da77b4 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1350,6 +1350,12 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) > if (WARN_ON_ONCE(!wbc->for_reclaim)) > goto redirty; > > + if (WARN_ON_ONCE(info->flags & VM_LOCKED)) > + goto redirty; Well, okay, I don't mind that. But shall we take bets on how soon syzbot (hope it's not watching) will try flipping SHM_LOCK on while swapping out pages from a SHM segment, and hit that warning? Perhaps I'm wrong, but I don't think any serialization prevents that. Hugh > + > + if (!total_swap_pages) > + goto redirty; > + > /* > * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "always" or > * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages, > @@ -1365,10 +1371,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) > } > > index = folio->index; > - if (info->flags & VM_LOCKED) > - goto redirty; > - if (!total_swap_pages) > - goto redirty; > > /* > * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC > -- > 2.39.1