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Sat, 29 Aug 2026 10:36:18 -0700 (PDT) From: Wenjie Qi To: willy@infradead.org, jack@suse.cz, akpm@linux-foundation.org Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, baohua@kernel.org, axboe@kernel.dk, trond.myklebust@hammerspace.com, tz2294@columbia.edu, qiwenjie@xiaomi.com, qwjhust@gmail.com Subject: [PATCH v3] mm: filemap: retain mapped dropbehind folios Date: Sun, 30 Aug 2026 01:36:12 +0800 Message-ID: <4aba05e1a2c3b61cb337d373eb9b7a8db4ddd822.1788024049.git.qiwenjie@xiaomi.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <3fa43eaca792bc0bbde4b82a6c1fcdd3f528b398.1787999152.git.qiwenjie@xiaomi.com> References: <20260820142956.1414337-1-qiwenjie@xiaomi.com> <3fa43eaca792bc0bbde4b82a6c1fcdd3f528b398.1787999152.git.qiwenjie@xiaomi.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Wenjie Qi Fault-around can map ready dropbehind folios without going through the normal page-cache lookup that clears dropbehind. A mapping represents a competing cached user, so retain the folio instead of forcibly unmapping it when writeback completes. For a mapped folio, folio_unmap_invalidate() can call unmap_mapping_folio(), which takes i_mmap_rwsem and may sleep. Retaining mapped folios avoids this path when folio_end_dropbehind() runs in non-preemptible task context. Unmapped dropbehind folios continue through the existing invalidation path. Fixes: fb7d3bc41493 ("mm/filemap: drop streaming/uncached pages when writeb= ack completes") Signed-off-by: Wenjie Qi Reviewed-by: Matthew Wilcox (Oracle) Reviewed-by: Tal Zussman --- Changes since v2: - Explain why retaining mapped folios avoids a sleepable unmap path. - Add the Fixes and Reviewed-by trailers. mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index 6afec636881f..00fd89cf6f55 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1616,7 +1616,7 @@ static void filemap_end_dropbehind(struct folio *foli= o) return; if (!folio_test_clear_dropbehind(folio)) return; - if (mapping) + if (mapping && !folio_mapped(folio)) folio_unmap_invalidate(mapping, folio, 0); } =20 --=20 2.43.0