* Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter [not found] ` <94a489d5-8b02-46e6-92d2-ccb85f556769@linux.dev> @ 2026-07-16 11:17 ` Ridong Chen 2026-07-17 2:27 ` Qi Zheng 0 siblings, 1 reply; 2+ messages in thread From: Ridong Chen @ 2026-07-16 11:17 UTC (permalink / raw) To: Qi Zheng, Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Chris Li, Kairui Song Cc: Muchun Song, Kemeng Shi, Nhat Pham, Baoquan He, Barry Song, Youngjun Park, David Hildenbrand, Lorenzo Stoakes, Axel Rasmussen, Yuanchu Xie, Wei Xu, Davidlohr Bueso, cgroups, linux-mm, linux-kernel, Ridong Chen, stable 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 <chenridong@xiaomi.com> >>>> >>>> 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? > >> } >> .... >> /* 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; >> } >> >> ... >> } >> ``` >> > -- Best regards Ridong ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter 2026-07-16 11:17 ` [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter Ridong Chen @ 2026-07-17 2:27 ` Qi Zheng 0 siblings, 0 replies; 2+ messages in thread From: Qi Zheng @ 2026-07-17 2:27 UTC (permalink / raw) To: Ridong Chen, Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Chris Li, Kairui Song Cc: Muchun Song, Kemeng Shi, Nhat Pham, Baoquan He, Barry Song, Youngjun Park, David Hildenbrand, Lorenzo Stoakes, Axel Rasmussen, Yuanchu Xie, Wei Xu, Davidlohr Bueso, cgroups, linux-mm, linux-kernel, Ridong Chen, stable 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 <chenridong@xiaomi.com> >>>>> >>>>> 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! ^ permalink raw reply [flat|nested] 2+ messages in thread
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2026-07-16 11:17 ` [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter Ridong Chen
2026-07-17 2:27 ` Qi Zheng
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