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b=bEJ25p44SexVsQl7zqgMU25xKTQUuw+NitGL8u3/G2PvC5JIz5916GmDjwDOSHENL U9eSqIO9ctB6EGOS/YBh/0p6bBvBJOPVtGCzZhXOEp1AHonBa318jyx77Byweb3nNO RFmy9gcW+3H3YD6a09ojeqj3kscTifU8gkWQy6wA= Date: Wed, 9 Sep 2026 10:49:39 -0700 From: Andrew Morton To: Youngjun Park Cc: Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , her0gyugyu@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 0/2] mm/swap: skip empty clusters in the swapoff scan Message-Id: <20260909104939.5203c02695fcfd7a95f4b26c@linux-foundation.org> In-Reply-To: <20260909161552.2335971-1-youngjun.park@lge.com> References: <20260909161552.2335971-1-youngjun.park@lge.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 685F240009 X-Stat-Signature: t6pii5x3k5ix4n9fiitaruadwjps9jpf X-HE-Tag: 1788976181-217133 X-HE-Meta: U2FsdGVkX1+ulD2T6eL/s2dRy5FVpsIr5pGe1NnW3+uWbW0TfyE8isTX6CfcM8saWsIiPUGYQgOG9vkHMyM0LZBZDxFxNUcUHke5WAfFfU1qtIz/0GIgE3CEKkC9w7YCsxEVOS5YUPMJhog1zKPIxSx6Sqxrn83RRTGIrROTakaNhgiwi9TzjxjWhEKuuDARV/LvzzUX5qcQyqBWnM0AyP2fw94YGo32D0dm6TdGNG0huzI7blQi3PdFIENjXhMXIbYQhCcV6kuA2MyXAoRAdlIi8hxsMAaSU3Qn+8+WmYRl3m+rr9x9OVa9st9kZJBAOLXPVdHqJIBj7Os6+AUvHSizMjk41ddGtMhGeo86L267KXlBVK5vcDW69KTctTtZVgmAStfEZpAFU8nO/5QHms48mpDQtHs3y2sIcwFLpp27jQjYTfNQmzfv9bkRrq4owU30AX2kkjT1VHzWXHJLslByodmsTbz6RtoRkX/lxMLOyFBkBxmJvrWy167xIV3XXiBpnb2nLErzT6wSm/0jH761A+FJO0ZZL4D8Qu0g7jcz57cGKdBsrgQww1n7ZxKdiVso74TkW1ujq4sufJQ3yxDlPN33w90TEcj1KjNnKdkGgzZcnB8tWmK7NNte4yyQTbwiO587kzUp+YHF1FlztiH/EfQJdE0oWb8FgsMwIjvpNaSZ9gP6KOMzDkxFla0yfSgvEHZrNMZb1f2XClY129EK0RuNB4vynEXZE4GJrDi1GRSYia4RjS0N3ECzczXlzf2dOOXEDygySiZC6xT3/R2jO+IxwmuihVLGGcMvN3PfUvHQF4aAB24nlKoX4pKgfTuDjEcH84pJsCFzVv3Je66wN5DDAg05mf4Kv9h1dvbk4w174Xwjh2FuGgUR7fftUZS5ZmKX5tvKn47JflqR6//xCv2XdWwmG9MT98Y0fRRC8J2Mv4kqZf0v5mLIY0F4RiGGYDxpb/aGmzdjL07 uB2BkKOt 1W5KYklNUvicTYh/y/blUpLSY6Y4qF1J4hbvwhY8b29OGWlw3xMiWG+z9BoxX+qGKkBqOYQC0U3KhqpWUO5+XI9DLaeYS12KGgir1Pp/IiZbDPqDDxWsJVc6gxU13rKYimknIw15niBc42JD69G5TRDq7d0cU6nFJgYqyaSVXgbnm6EvIpAfDrIBg5IGTYwOogjDI7ZIgcOtLqNwRsW3T6kFgb5es4l8xtAVO0mGqmda32ZiuTNMEduRwEoWNXSTJfqMeuXKc0c+U0e7cRugjOBaliw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 10 Sep 2026 01:15:50 +0900 Youngjun Park wrote: > find_next_to_unuse() walks a swap device one offset at a time. Slot > state now lives in a per cluster swap table, so patch 2 dismisses an > empty cluster with one counter read instead of SWAPFILE_CLUSTER table > reads. > > Patch 1 is an unrelated one line comment fix noticed on the way. > > A debug test confirmed the skip path runs, and swapoff completed > under load with no DEBUG_VM or lockdep splats. Please let's try to make the [0/N] words provide a summary of the patchset's effects. The above didn't even tell people that this is a swapoff optimization! I asked an LLM for this summary and we came up with : Speed up swapoff and reduce scanning stalls on large, mostly empty : swap devices by skipping empty clusters. Reduce swapoff time on a 1 : TiB device from 158 ms to 94 ms after filling 128 GiB, and from 392 : ms to 73 ms after filling 512 GiB; expect little benefit when : substantial swap data remains. Does that sound OK?