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[70.77.200.158]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82b03bc1e59sm15996602b3a.13.2026.03.25.03.15.53 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Mar 2026 03:15:53 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.100.1.1.5\)) Subject: Re: [RFC 1/1] ext4: fail fast on repeated metadata reads after IO failure From: Andreas Dilger In-Reply-To: <20260325093349.630193-2-diangangli@gmail.com> Date: Wed, 25 Mar 2026 04:15:42 -0600 Cc: tytso@mit.edu, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, changfengnan@bytedance.com, Diangang Li Content-Transfer-Encoding: 7bit Message-Id: References: <20260325093349.630193-1-diangangli@gmail.com> <20260325093349.630193-2-diangangli@gmail.com> To: Diangang Li X-Mailer: Apple Mail (2.3864.100.1.1.5) On Mar 25, 2026, at 03:33, Diangang Li wrote: > > From: Diangang Li > > ext4 metadata reads serialize on BH_Lock (lock_buffer). If the read fails, > the buffer remains !Uptodate. With concurrent callers, each waiter can > retry the same failing read after the previous holder drops BH_Lock. This > amplifies device retry latency and may trigger hung tasks. > > In the normal read path the block driver already performs its own retries. > Once the retries keep failing, re-submitting the same metadata read from > the filesystem just amplifies the latency by serializing waiters on > BH_Lock. > > Remember read failures on buffer_head and fail fast for ext4 metadata reads > once a buffer has already failed to read. Clear the flag on successful > read/write completion so the buffer can recover. ext4 read-ahead uses > ext4_read_bh_nowait(), so it does not set the failure flag and remains > best-effort. Not that the patch is bad, but if the BH_Read_EIO flag is set on a buffer and it prevents other tasks from reading that block again, how would the buffer ever become Uptodate to clear the flag? There isn't enough state in a 1-bit flag to have any kind of expiry and later retry. Cheers, Andreas