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From: Qi Zheng In-Reply-To: <65305712-8598-46aa-822b-914298277b64@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D8E2420007 X-Stat-Signature: 9nr3f7x7gxwih9fw59s7akre96cfrfxn X-HE-Tag: 1784255291-357761 X-HE-Meta: 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 MJiF9yVu k0at9jYW5FcxuYoR9ciW0qm7DEsmhbneIVXNBhwtpnYz8L2lJ+hktNxtctQdT2gJk2RRkYxfyOFX9+bs62EwaNS07k4YTDWGptqWuQzhHkQTZiuQz9Jf1t1a3Pbf3g96jdwgdjhMrdDj14oIvSocxdyu4a3gzcDpJZc9ik8rFAZE6HqInERQYt4IPYlFO2zkXL8auumJ089m0QUUaO4KtCQgIKavsSMdIdR97rVHduMUaVFqjpFmLRM97rxzEHaeDNj49 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/16/26 7:17 PM, Ridong Chen wrote: > > > On 7/16/2026 4:42 PM, Qi Zheng wrote: >> >> >> On 7/16/26 4:21 PM, Ridong Chen wrote: >>> >>> >>> On 7/16/2026 11:58 AM, Qi Zheng wrote: >>>> Hi Ridong, >>>> >>>> On 7/16/26 11:17 AM, Ridong wrote: >>>>> From: Ridong Chen >>>>> >>>>> sc_swappiness() had two separate definitions depending on >>>>> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned >>>>> vm_swappiness, ignoring the proactive_swappiness value passed >>>>> through scan_control. This caused the swappiness parameter >>>>> written to /sys/devices/system/node/nodeX/reclaim to have no >>>>> effect when CONFIG_MEMCG is disabled. >>>>> >>>>> Fix this by consolidating sc_swappiness() into a single definition >>>>> that checks sc->proactive_swappiness first, then falls back to >>>>> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG >>>>> and !CONFIG_MEMCG. >>>>> >>>>> Before fix (swappiness=max ignored, mostly file pages reclaimed): >>>>> >>>>>      # cat /proc/sys/vm/swappiness >>>>>      60 >>>>>      # cat /proc/vmstat | grep pgsteal >>>>>      pgsteal_kswapd 0 >>>>>      pgsteal_direct 0 >>>>>      pgsteal_khugepaged 0 >>>>>      pgsteal_proactive 1840 >>>>>      pgsteal_anon 25 >>>>>      pgsteal_file 1815 >>>>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/ >>>>> reclaim >>>>>      # cat /proc/vmstat | grep pgsteal >>>>>      pgsteal_kswapd 0 >>>>>      pgsteal_direct 0 >>>>>      pgsteal_khugepaged 0 >>>>>      pgsteal_proactive 18013 >>>>>      pgsteal_anon 337 >>>>>      pgsteal_file 17676 >>>>> >>>>> After fix (swappiness=max honored, anon pages reclaimed as expected): >>>>> >>>> >>>> By the way, in get_scan_count(), it seems we still reclaim file pages >>>> without swap space, even if swappiness=max (SWAPPINESS_ANON_ONLY) is >>>> set. >>>> >>>> This behavior appears to contradict the semantics of >>>> SWAPPINESS_ANON_ONLY, which probably needs a fix as well. >>>> >>> Thanks, Qi. >>> >>> You're right. Currently, when can_reclaim_anon_pages() returns false, >>> the reclaim logic falls back to scanning file folios even if >>> swappiness == SWAPPINESS_ANON_ONLY is set: >>> >>> ``` >>> static void get_scan_count(struct lruvec *lruvec, struct scan_control >>> *sc, >>>                 unsigned long *nr) >>> { >>>      .... >>>      /* If we have no swap space, do not bother scanning anon folios. */ >>>      if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat- >>> >node_id, sc)) { >>>          scan_balance = SCAN_FILE; >>>          goto out; >>>      } >>> >>>      ... >>>      /* Proactive reclaim initiated by userspace for anonymous memory >>> only */ >>>      if (swappiness == SWAPPINESS_ANON_ONLY) { >>>          WARN_ON_ONCE(!sc->proactive); >>>          scan_balance = SCAN_ANON; >>>          goto out; >>>      } >>>      ... >>> } >>> ``` >>> >>> The !can_reclaim_anon_pages() check above takes precedence over the >>> SWAPPINESS_ANON_ONLY branch, making the latter effectively >>> unreachable when anonymous pages are deemed non-reclaimable. >>> >>> To fix this, could we move the SWAPPINESS_ANON_ONLY check up before >>> the can_reclaim_anon_pages() check? >>> >>> ``` >>> static void get_scan_count(struct lruvec *lruvec, struct scan_control >>> *sc, >>>                 unsigned long *nr) >>> { >>>      ... >>>      /* Proactive reclaim initiated by userspace for anonymous memory >>> only */ >>>      if (swappiness == SWAPPINESS_ANON_ONLY) { >>>          WARN_ON_ONCE(!sc->proactive); >>>          scan_balance = SCAN_ANON; >>>          goto out; >> >> For SWAPPINESS_ANON_ONLY + !can_reclaim_anon_pages, perhaps we should >> just return directly instead of goto out, since no pages can be >> reclaimed in this situation. >> > > Much better. > Would you mind if I send a separate patch to fix this issue? > Sure, thanks for your time on this, and I look forward to your fix!