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From: Ridong Chen In-Reply-To: <94a489d5-8b02-46e6-92d2-ccb85f556769@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: bays7q1fk4gjw7ewd8xqnf5h1kqem5g7 X-Rspamd-Queue-Id: E55321A0005 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1784200640-864514 X-HE-Meta: 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 JRJrRH7J 6k5Zfj7FpDUrzd5EAvb+/sVEJEzt/DpszDFUS7I7pkDhD9AZR3+F2ioG0lrmk5yKovBk5LKmIehVeWQhsGo+sjr7k34O+T5uMHfzGwblWfDXntJqSloymEVtJp1Oy79kkv1imXd49XqNF1OVT099LpAOzKVlAewte6WhaDnMUrsEpu/9UWhL3Li7Tyb5D/LBSY5p3WdVeueuTsqZO33ONueIXms8+6HBSPrnFKj/AfmawTYkYqhSMF5yh2yxeuikpQItS7l5fiMFB+78= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? > >>      } >>      .... >>      /* 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