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Tue, 20 Jan 2026 07:01:54 -0800 (PST) Message-ID: <322136ff-95f6-49f6-9126-05845f25b4e8@kernel.dk> Date: Tue, 20 Jan 2026 08:01:52 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Fwd: [PATCH v2] bcache: use bio cloning for detached device requests To: Coly Li , Stephen Zhang Cc: Kent Overstreet , Sasha Levin , Christoph Hellwig , linux-bcache@vger.kernel.org, Linux Kernel Mailing List , zhangshida References: <20260120023535.9109-1-zhangshida@kylinos.cn> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/20/26 7:46 AM, Coly Li wrote: >> @@ -949,6 +950,11 @@ static int bcache_device_init(struct >> bcache_device *d, unsigned int block_size, >> BIOSET_NEED_BVECS|BIOSET_NEED_RESCUER)) >> goto out_ida_remove; >> >> + if (bioset_init(&d->bio_detach, 4, > ^^^^^-> I feel 4 might be a bit small > here. bio_detached set is for normal IO when backing device is not > attached to a cache device. I would suggest to set the pool size to > 128 or 256. Absolutely not, 4 is more than plenty. The pool elements are only ever used if allocations fail, to guarantee forward progress. Setting aside 128 or 256 for that case is utterly wasteful, you only need a couple. 4 is a good number, if anything it should be smaller (2). -- Jens Axboe