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Wong" , Carlos Maiolino , Alexander Viro , Jan Kara , Christoph Hellwig , Dave Chinner , Bart Van Assche , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Gao Xiang Subject: Re: [PATCH v6 3/4] buffer: add dropbehind writeback support Message-ID: References: <20260514-blk-dontcache-v6-0-782e2fa7477b@columbia.edu> <20260514-blk-dontcache-v6-3-782e2fa7477b@columbia.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspam-User: X-Rspamd-Queue-Id: 2BA5F4000D X-Stat-Signature: xaxhzz64o5877zyo4btqy79jfsq7dap6 X-Rspamd-Server: rspam06 X-HE-Tag: 1779686745-722464 X-HE-Meta: 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 gwOos88H 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 22, 2026 at 07:14:46PM -0400, Tal Zussman wrote: > > if (IS_ERR(folio)) > > return PTR_ERR(folio); > > @@ -2160,6 +2165,13 @@ int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len, > > *foliop = folio; > > return status; > > } > > Q: "Is an EXPORT_SYMBOL() or EXPORT_SYMBOL_GPL() needed for > block_write_begin_iocb()? > Since the legacy wrapper block_write_begin() remains exported, it appears > filesystems compiled as loadable modules (like ext4 or fat) will encounter > linker errors if they attempt to transition to the new API." > > A: Can be added once filesystems want to use it. Yeah, Sashiko is really stupid and counterproductive here. > > @@ -2715,6 +2727,9 @@ static void submit_bh_wbc(blk_opf_t opf, struct buffer_head *bh, > > > > bio = bio_alloc(bh->b_bdev, 1, opf, GFP_NOIO); > > > > + if (folio_test_dropbehind(bh->b_folio)) > > + bio_set_flag(bio, BIO_COMPLETE_IN_TASK); > > + > > Q: "Does this add unnecessary workqueue overhead for read operations? > While task-context deferral is required for asynchronous writeback completions > to allow folio_end_writeback() to sleep and invalidate the folio, read > dropbehind invalidation is handled synchronously in the reader's task context > via filemap_end_dropbehind_read(). > Could this be gated by an op == REQ_OP_WRITE or op_is_write(opf) check so > that read bio completions aren't forced into a workqueue?" > > A: Seems worth adding a op_is_write(opf) check to avoid deferring read > dropbehind completions. Yes.