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bh=7y3NOM7xqvWmL65AFq+ZWC79CgE7opPLQwAIectARfc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=essh9OvEhCNgIzvXj70luMYDVXtcP8DELRtgMlhe1mMVJnzfaVGUkxkYbOPRmTL8D OGUqMGkYVSgbRgupoV8D/5a+w+s6wsnLtP1XfgxGHzcGCXPwRTGP7YrTSTONWKRCzp ImUT0DzjRA74z3ukf+xedel4OBNzDoykCxxg5TX81/qvSPy7dAPVJsQZf9W9jjMf+4 DvNkhL1xMliJLz9ZMTlIhD5wdz8dw2PFfkgGXfxNlfQzi/vxAO0OVYvkOFftRIQl2L BV2u2yshAT72wI+uW+QCFE8gOH6AJivte2T9movH2sbplMjbA8Ah0YHlbspTiyWvPL YBgF2o/in2O6w== From: Mike Snitzer To: Chuck Lever , Jeff Layton Cc: linux-nfs@vger.kernel.org, NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Christoph Hellwig , Jens Axboe , Matthew Wilcox , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v5 3/6] mm: add folio_mark_dropbehind() to mark a folio dropbehind and account it Date: Mon, 19 Oct 2026 11:07:22 -0400 Message-ID: <20261019150725.1507-4-snitzer@kernel.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20261019150725.1507-1-snitzer@kernel.org> References: <20261019150725.1507-1-snitzer@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: mk9zipm9g3q6wak73d4ardoyxsgysgua X-Spam-Status: No, score=-19.1 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, RCVD_IN_DNSWL_BLOCKED,RCVD_IN_ZEN_BLOCKED_OPENDNS,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 7516C18000A X-Rspam-User: X-HE-Tag: 1792422451-488851 X-HE-Meta: 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 MNY1J1vw H9x1AOtvU1UQMdJALFcn2FRbTW2wAZCb7cPyn+I1jznbHg5T42enVog4Z53jjomfSJwZnc9L/9Drbrmta+T/zZ4iAI9ORdVl39qUNQXne8Rj/kTFaNBPOQjR6vKaLl+kUr1BtbhLSlayJY86eEmubse4wmL+aEusLGSyMFECe6I7+ABDJn5urm/OMg2bRwxB3vaIl+SgDEIXmXaTNtElBzEFm4IFqlCCQtyYj8RzLxW/PBpy8ytOVdXUuPLRkl9r2saZt8IQ6IvZVtKJDPRDQut5Xg+5cgUacYz4skyScN5xXnRW7LppY/+/ZE6CtztzEBtLaHC9ORoOOtNjeCRHDmDidu4yxUqazhFue4V5a4VbqZ3v/cw8aT8j3CVgB8Xoqj6oP99i1r6Cvuog2Lz7AzSIpB5Fp8q0/UjEeCmh0w0mcPjiklWPRo6VkW9ZGfVlABgJNIOkBAoI7BFHovG0XhzSj4tnyNOP6Lwg3 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 A folio allocated by an RWF_DONTCACHE write is marked dropbehind before it is dirtied, so folio_account_dirtied() adds it to WB_DONTCACHE_DIRTY and folio_clear_dirty_for_io() or folio_account_cleaned() subtracts it when it is cleaned. Nothing marks a folio that already exists. A caller that sets PG_dropbehind on a folio that is already dirty unbalances the counter: the clean subtracts what was never added, and once the counter goes negative, wb_stat_sum() reads it as zero and the DONTCACHE writeback kick stops writing anything back for every writer on that bdi_writeback. Add folio_mark_dropbehind(), the inverse of the clear in __filemap_get_folio_mpol(): with the folio locked, mark it and, if it is dirty, add it to WB_DONTCACHE_DIRTY. The folio lock orders this against dirtying and against folio_clear_dirty_for_io(). A concurrent lookup without FGP_DONTCACHE that clears the flag again subtracts what this added. The name follows folio_set_dirty() and folio_mark_dirty(): the first only sets PG_dirty, the second also accounts the dirty folio. folio_set_dropbehind() likewise only sets PG_dropbehind, and folio_mark_dropbehind() also accounts it in WB_DONTCACHE_DIRTY. A later commit uses it in NFSD to drop a page shared by two misaligned WRITEs once both have written it. Cc: Jeff Layton Cc: Jens Axboe Cc: Matthew Wilcox (Oracle) Cc: linux-mm@kvack.org Assisted-by: LLM Signed-off-by: Mike Snitzer --- include/linux/pagemap.h | 1 + mm/filemap.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 0adfa6605653..3012bd95812a 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1310,6 +1310,7 @@ 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 00fd89cf6f55..ed7e4dbea653 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1644,6 +1644,37 @@ 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. A folio that + * is already dirty is added to WB_DONTCACHE_DIRTY, as folio_account_dirtied() + * would have added it had it been marked when dirtied, so that the clean + * that subtracts it leaves the counter balanced. + */ +void folio_mark_dropbehind(struct folio *folio) +{ + struct address_space *mapping = folio->mapping; + + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); + + if (folio_test_dropbehind(folio)) + return; + folio_set_dropbehind(folio); + if (mapping && folio_test_dirty(folio) && + mapping_can_writeback(mapping)) { + struct inode *inode = mapping->host; + struct bdi_writeback *wb; + struct wb_lock_cookie cookie = {}; + + wb = unlocked_inode_to_wb_begin(inode, &cookie); + wb_stat_mod(wb, WB_DONTCACHE_DIRTY, folio_nr_pages(folio)); + unlocked_inode_to_wb_end(inode, &cookie); + } +} +EXPORT_SYMBOL_GPL(folio_mark_dropbehind); + /** * folio_end_writeback_no_dropbehind - End writeback against a folio. * @folio: The folio. -- 2.52.0