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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pPF2L-00HQc1-GG; Tue, 07 Feb 2023 03:52:53 +0000 Date: Tue, 7 Feb 2023 03:52:53 +0000 From: Matthew Wilcox To: Luis Chamberlain Cc: hughd@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, p.raghav@samsung.com, dave@stgolabs.net, a.manzanares@samsung.com, linux-kernel@vger.kernel.org Subject: Re: [RFC 1/2] shmem: set shmem_writepage() variables early Message-ID: References: <20230207025259.2522793-1-mcgrof@kernel.org> <20230207025259.2522793-2-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230207025259.2522793-2-mcgrof@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 74E9080004 X-Stat-Signature: aoqbt3ixp3jq4x9t85bynby9aau34pxy X-HE-Tag: 1675741980-406418 X-HE-Meta: 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 /KZLyalm 1AxUdxFs2YJ62FAzPSq/Meem7jC7yJ4QN3GTO6UZ07PF+bLxDYmazmMq7JMYJCYJoyfMs9drk5rDOhPNNLdqi61I2mjIp5vA1F3gMT5x0w9LUOESTpd18Yk+PxCi3qw2tPkrZdYkikB8EpRrt7T5vNJpoZ0QsTXJVRxL9b6+tY1VUhsNpCEEnzmlM+gP5xN8YQJXCIt7YVV7KZpX7gyUAaYYlp4gcH4rKL2/xQbISW5OKmFkSiHh26S/nm8osCDTtrLKE 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 Mon, Feb 06, 2023 at 06:52:58PM -0800, Luis Chamberlain wrote: > shmem_writepage() sets up variables typically used *after* a possible > huge page split. However even if that does happen the address space > mapping should not change. So it should be safe to set that from > the beginning. Yes, we can get mapping from the folio early. It doesn't change on split. > The folio should always be locked from the start as well. It however > was not clear if the folio address can / should change, as well as > the first inode. > > This commit makes no functional changes other a double check on the > folio locking which might be superflous. This change should help make > the subsequent patch easier to review. You don't need to check that the folio's locked, and you don't need to reassign inode after the split. > Signed-off-by: Luis Chamberlain > --- > mm/shmem.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 28f3c699c8ce..a2c6aa11aab8 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1332,11 +1332,13 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) > { > struct folio *folio = page_folio(page); > struct shmem_inode_info *info; > - struct address_space *mapping; > - struct inode *inode; > + struct address_space *mapping = folio->mapping; > + struct inode *inode = mapping->host; > swp_entry_t swap; > pgoff_t index; > > + BUG_ON(!folio_test_locked(folio)); > + > /* > * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "always" or > * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages, > @@ -1351,8 +1353,8 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) > folio_clear_dirty(folio); > } > > + /* Can the folio or first inode change on after a split? */ > BUG_ON(!folio_test_locked(folio)); > - mapping = folio->mapping; > index = folio->index; > inode = mapping->host; > info = SHMEM_I(inode); > -- > 2.39.0 >