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b=Nb9+nB6aRZWS+S6IFgOz5cLkH9/xjbELLeESlrJs0i/rdpYbDCRNvcds+kdyGev8d 2BwgmTejaL5H3uVCYwd1vgkNqzIWxNHIAJgQp7wIwZpEveD5HV10UZ47btuxRVHx6P zqP7kGmEBkPTQI/6sMUzOnYDBvgQnbU8zY90spr/gHyCNupyN5VWzofhBfsNH6h5yt fcj+gbhHZr+e1aUNV1hcMfLqxIoH0I01JJyO3rUmaOYBc86TDIjh4nT6eRRshCNIp2 iy6N/rsb2YZ6F96qy42GBK+7aeb5StJQ+wKXcYZdsrOLRAy8yMM9/AyZQiVe97YpjQ QsofTWMKIvfQA== From: Mike Snitzer To: Matthew Wilcox , Jan Kara , linux-mm@kvack.org, Christian Brauner , linux-fsdevel@vger.kernel.org Cc: Chuck Lever , Jeff Layton , linux-nfs@vger.kernel.org Subject: [PATCH v11 4/7] mm: add folio_mark_dropbehind() to mark a folio dropbehind and account it Date: Tue, 10 Nov 2026 20:56:04 -0500 Message-ID: <20261111015607.46338-5-snitzer@kernel.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20261111015607.46338-1-snitzer@kernel.org> References: <20261111015607.46338-1-snitzer@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Stat-Signature: dcighxkmm95faaysou73x8474ksrnedr X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: E5CE9C0005 X-Rspam-User: X-HE-Tag: 1794362174-849225 X-HE-Meta: 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 nwO0P6Me 3XISU1wLjaiLK3PzfVSIo2/OZTI3fEyi31v1C4SUX7cJvaF5UOyhG1LFW1tj8YFWcNScdiAfhRDITg/FSa0hRfehsVpDZwU4x4/fdaqjlZCaF9J5/ohxgutg5FIzb6JQ/VrU/Esbaslt6ckVxUC7jQMARhBjnH7Zv0cxrsN7OWGAV0imDh0HJJ+xXjwUTuHEe6lXvvZ3RxHZ7QhvIyrPbC1xhD6hrTLNJr5qskzKG2nMIEvbvpaO7DMUxzk5MmmCcio71r94En2hlauMLYGB2+Oa7gQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 WB_DONTCACHE_DIRTY counts the dirty folios that are marked dropbehind. When a dropbehind folio is dirtied, folio_account_dirtied() adds it to the counter. When the folio is cleaned, folio_clear_dirty_for_io() or folio_account_cleaned() subtracts it again. This balances only if the folio is marked before it is dirtied, as it is for the folios that an RWF_DONTCACHE write creates. To prepare for NFSD to mark a folio dropbehind once both writes that share it have written their parts, handle a folio that is already dirty when it is marked. folio_set_dropbehind() only sets the flag. With it, the clean would subtract the folio from WB_DONTCACHE_DIRTY although it was never added, and the counter would go negative. Add folio_mark_dropbehind(), the inverse of filemap_clear_dropbehind(). With the folio locked, it sets PG_dropbehind. Under the i_pages lock, it adds the folio to WB_DONTCACHE_DIRTY if both PG_dirty and the dirty tag are set. A dirtier that has set PG_dirty but not yet counted the folio finds the flag set and counts the folio itself. The name follows folio_set_dirty() and folio_mark_dirty(): the set variant only sets the flag, the mark variant also accounts for it. Reviewed-by: Jeff Layton Signed-off-by: Mike Snitzer --- include/linux/pagemap.h | 1 + mm/filemap.c | 32 ++++++++++++++++++++++++++++++++ 2 files changed, 33 insertions(+) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 73af18a373670..3f5295d6fd73b 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1306,6 +1306,7 @@ void end_page_writeback(struct page *page); void folio_end_writeback(struct folio *folio); void folio_end_writeback_no_dropbehind(struct folio *folio); void folio_end_dropbehind(struct folio *folio); +void folio_mark_dropbehind(struct folio *folio); void folio_wait_stable(struct folio *folio); void __folio_mark_dirty(struct folio *folio, struct address_space *, int warn); void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb); diff --git a/mm/filemap.c b/mm/filemap.c index 98ce955404127..a54d0fbd37222 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1654,6 +1654,38 @@ void folio_end_dropbehind(struct folio *folio) } EXPORT_SYMBOL_GPL(folio_end_dropbehind); +/** + * folio_mark_dropbehind - mark an existing folio dropbehind + * @folio: the folio, locked by the caller + * + * Mark @folio so that the writeback that cleans it drops it. If the folio + * is already counted as dirty, which with the i_pages lock held means both + * PG_dirty and the dirty tag are set, add it to WB_DONTCACHE_DIRTY so that + * the clean that subtracts it leaves the counter balanced. + */ +void folio_mark_dropbehind(struct folio *folio) +{ + struct address_space *mapping = folio->mapping; + unsigned long flags; + + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); + + if (folio_test_dropbehind(folio)) + return; + if (!mapping || !mapping_can_writeback(mapping)) { + folio_set_dropbehind(folio); + return; + } + xa_lock_irqsave(&mapping->i_pages, flags); + folio_set_dropbehind(folio); + if (folio_test_dirty(folio) && + xa_get_mark(&mapping->i_pages, folio->index, PAGECACHE_TAG_DIRTY)) + wb_stat_mod(inode_to_wb(mapping->host), WB_DONTCACHE_DIRTY, + folio_nr_pages(folio)); + xa_unlock_irqrestore(&mapping->i_pages, flags); +} +EXPORT_SYMBOL_GPL(folio_mark_dropbehind); + /** * folio_end_writeback_no_dropbehind - End writeback against a folio. * @folio: The folio. -- 2.52.0