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Thu, 25 Jun 2026 04:31:50 -0700 (PDT) Message-ID: <1358cfd4-7d3f-1238-e4a8-b2301dc16702@gmail.com> Date: Thu, 25 Jun 2026 19:31:40 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.0 Subject: Re: [PATCH v4 1/5] mm/zswap: Extend shrink_memcg() writeback capability To: Yosry Ahmed Cc: akpm@linux-foundation.org, tj@kernel.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, mhocko@kernel.org, mkoutny@suse.com, nphamcs@gmail.com, chengming.zhou@linux.dev, muchun.song@linux.dev, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Hao Jia References: <20260618044857.69439-1-jiahao.kernel@gmail.com> <20260618044857.69439-2-jiahao.kernel@gmail.com> <057ea303-4c27-1a6e-08de-cce26c699097@gmail.com> From: Hao Jia In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E1A49140006 X-Rspam-User: X-Stat-Signature: p5hhtubaxbzpnjzd47gsotpwushn87si X-HE-Tag: 1782387111-705732 X-HE-Meta: U2FsdGVkX1/TS6uHvGTUkZKwGTxSOczNZp3haMr+1bIQ9zhBz6qgokaRPLtKfO2NS9l+p0tJVCO7oyf8cZPaKdK1COwVe3PduzVa0iUuWwdBZhcMuj+9VhRNfrYJack4yISdlTBKLrSqPYQwFR7mBCTdBvPactOr92QLybZPX/i2GIx4cthc85eKyVPgmOSC9GD15gXPbAaB8pIfnwtBD6OOe/nF/TLl20TqGjc7ze+BeN0iFAGKAxbfp3NP7ikIAM+50DTvNWg5ICB65vQC/CYhI8/IMgAGNVH2T4/DbDofDGvE0gGBR33dmuzCiKCoSJTj9NQ1uopLxO45pTCUsirWgA6qhMBS/g236XTvx/vK5DUuntECWQR0Hnjp+ivWfK71vQKFsRObzIyjfDuDTyVAJUbGLbb58e/dmvTNCe1O6685AlZ2RQmFVmq63JRvZeFimdQn0vyxmuOQmSupJ5xZrTNkWro4YEa81uiOAPYpq+pNqYDBs/YjYMxwWY8UA0h4GJl0R2G6dBzzjm467RUA/XHHBNy0dW12bsQgjUEsSbEId7Orn0mvb7BkA9kuF3qRxqw8BfwhU1n8o2l/q05J9ipjLLtHEpyXKXP0s9IzYNWyk8Peq6gItvsp3fAgXtlvVr0t6kFmtd1DOyCM0t25Q5xS4iMrFUm/RYApWI6wpOigybTwiZPKWKIhHuUSYOmLxpoLpfUPhDimlDl7dFW9ggSzYD9Af0ZWJ3Rrx4LoHSx+i+KBxGjKHzS/zoaqRrkQMUKAdgy7iImUey/2lU9aAtfi1SRrCJzInWvSzRO5cgYy74jbEDniIpDsTmdZlA6EBe14Yy3Qcg4yDLBcyQ9x3LtM92Bbm8rzkU397cPN9t5EFf8bDnD/OUmh3dYyA2rwfPrJlunGLk5m4X7NwL9kwWQoAlETztLAj37p+4fIjYu9pLoaeDKQmucKXgaXLt+ZIKF/BTb265l2fmz 0G+dl3pr c+4UcypTfo6nwaUSuCtRh+LxOO5FwL4V0DdJU4MkGhYEJRD8m7/UKh9BtYRDaXZDpHuJEWksRFAVgHua7LLq6oPzsufbN23xWuZw9bo2+OmOmC2uEvMcIZkTLu4vbgjKjE+/cBMYrQToceIGR5b+T9QQjnNKNwktmXbGIESTh8YzMlua1GSIH4BnVIGpYMbwS0ktFbzOOdtQaACqAXF7J7Aam6eFKGdAKz2tdZCYfH6ZFnGqkUAhoazx7eDVGSeeUoPS+fRBrxQCu64rKjq1j8xKBN5RPKWiR8JmslSS5MwBcPWLjdTvXOnQTh1lyOi10HF91ZcEE9eGmJw5KJb8YGP3cDxrL+V4LLLHlg1xpXsTMT+3dBNgeegQNuxXAbFc2dDqCVBdjXKPp5d9WlRUFiaA+492czSP6abedPi4NsUqwJ78bj83VTz6BzNekFFKORJR2nKSmQs0wXGgax2HVWRVf2WbskX9tOJ3XIKSoLOlc0ok= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/6/25 00:57, Yosry Ahmed wrote: >> >> /* >> * Scan up to @nr_to_scan pages across the per-node zswap LRUs of @memcg >> * and write back the reclaimable ones. >> * >> * Since the second-chance algorithm rotates referenced entries to the >> * LRU tail, the per-node scan is capped at the current LRU length so >> * each entry is scanned at most once per call. It is up to the caller >> * to handle retries, deciding whether to scan the next memcg to complete > > Nit: "whether to scan another memcg to complete.." Will fix in the next version. > >> * the full iteration, or to rescan the current memcg to drain its zswap >> * entries. >> * >> * Return: The number of compressed bytes written back (>= 0), or -ENOENT >> * if @memcg has writeback disabled, is a zombie cgroup, or has empty >> * zswap LRUs. >> */ >> static long shrink_memcg(struct mem_cgroup *memcg, unsigned long nr_to_scan) >> { >> struct zswap_shrink_walk_arg walk_arg = { >> .bytes_written = 0, >> .encountered_page_in_swapcache = false, >> }; >> unsigned long nr_remaining = nr_to_scan; >> int nid; >> >> if (!mem_cgroup_zswap_writeback_enabled(memcg)) >> return -ENOENT; >> >> /* >> * Skip zombies because their LRUs are reparented and we would be >> * reclaiming from the parent instead of the dead memcg. >> */ >> if (memcg && !mem_cgroup_online(memcg)) >> return -ENOENT; >> >> for_each_node_state(nid, N_NORMAL_MEMORY) { >> unsigned long nr_to_walk; >> >> /* >> * Cap the walk at the current LRU length to ensure each entry is >> * scanned at most once per call. Referenced entries are rotated >> * to the tail for a second chance, and this bound prevents them >> * from being revisited within a single call. Retries are left to >> * the caller, which can choose to rescan the current memcg or >> * move on to the next one. >> */ > > Nit: Make this more concise since it's already explained above. > Will fix in the next version. Thanks a lot for the review! Thanks, Hao > Otherwise this looks good to me, thank you! > >> nr_to_walk = min(nr_remaining, >> list_lru_count_one(&zswap_list_lru, nid, memcg)); >> if (!nr_to_walk) >> continue; >> >> nr_remaining -= nr_to_walk; >> list_lru_walk_one(&zswap_list_lru, nid, memcg, &shrink_memcg_cb, >> &walk_arg, &nr_to_walk); >> /* Return the unused share of the budget to the pool. */ >> nr_remaining += nr_to_walk; >> >> if (!nr_remaining) >> break; >> } >> >> /* Nothing was scanned: every LRU under @memcg was empty. */ >> if (nr_remaining == nr_to_scan) >> return -ENOENT; >> >> return walk_arg.bytes_written; >> } >>