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Tue, 09 Sep 2025 10:25:02 -0700 (PDT) Message-ID: Date: Tue, 9 Sep 2025 11:25:02 -0600 Precedence: bulk X-Mailing-List: linux-raid@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [GIT PULL v2] md-6.18-20250909 To: Yu Kuai , linux-block@vger.kernel.org, linux-raid@vger.kernel.org Cc: linan122@huawei.com, xni@redhat.com, colyli@kernel.org, yukuai3@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com References: <20250909171328.2691074-1-yukuai@kernel.org> Content-Language: en-US From: Jens Axboe In-Reply-To: <20250909171328.2691074-1-yukuai@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/9/25 11:13 AM, Yu Kuai wrote: > Hi, Jens > > Redundant data is used to enhance data fault tolerance, and the storage > method for redundant data vary depending on the RAID levels. And it's > important to maintain the consistency of redundant data. > > Bitmap is used to record which data blocks have been synchronized and which > ones need to be resynchronized or recovered. Each bit in the bitmap > represents a segment of data in the array. When a bit is set, it indicates > that the multiple redundant copies of that data segment may not be > consistent. Data synchronization can be performed based on the bitmap after > power failure or readding a disk. If there is no bitmap, a full disk > synchronization is required. > > Due to known performance issues with md-bitmap and the unreasonable > implementations: > > - self-managed IO submitting like filemap_write_page(); > - global spin_lock > - ... > > I have decided not to continue optimizing based on the current bitmap > implementation, this new bitmap is invented without locking from IO fast > path and can be used with fast disks. > > Key features for the new bitmap: > - IO fastpath is lockless, if user issues lots of write IO to the same > bitmap bit in a short time, only the first write has additional > overhead to update bitmap bit, no additional overhead for the following > writes; > - support only resync or recover written data, means in the case creating > new array or replacing with a new disk, there is no need to do a full > disk resync/recovery; Much better! Though I suspect you forgot to add more where you have the "..." above, I just removed it. Pulled, thanks. -- Jens Axboe