mm: memcg: per-priority per-zone hierarchy scan generations
Memory cgroup limit reclaim currently picks one memory cgroup out of the target hierarchy, remembers it as the last scanned child, and reclaims all zones in it with decreasing priority levels. The new hierarchy reclaim code will pick memory cgroups from the same hierarchy concurrently from different zones and priority levels, it becomes necessary that hierarchy roots not only remember the last scanned child, but do so for each zone and priority level. Until now, we reclaimed memcgs like this: mem = mem_cgroup_iter(root) for each priority level: for each zone in zonelist: reclaim(mem, zone) But subsequent patches will move the memcg iteration inside the loop over the zones: for each priority level: for each zone in zonelist: mem = mem_cgroup_iter(root) reclaim(mem, zone) And to keep with the original scan order - memcg -> priority -> zone - the last scanned memcg has to be remembered per zone and per priority level. Furthermore, global reclaim will be switched to the hierarchy walk as well. Different from limit reclaim, which can just recheck the limit after some reclaim progress, its target is to scan all memcgs for the desired zone pages, proportional to the memcg size, and so reliably detecting a full hierarchy round-trip will become crucial. Currently, the code relies on one reclaimer encountering the same memcg twice, but that is error-prone with concurrent reclaimers. Instead, use a generation counter that is increased every time the child with the highest ID has been visited, so that reclaimers can stop when the generation changes. Signed-off-by: NJohannes Weiner <jweiner@redhat.com> Reviewed-by: NKirill A. Shutemov <kirill@shutemov.name> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Cc: Balbir Singh <bsingharora@gmail.com> Cc: Ying Han <yinghan@google.com> Cc: Greg Thelen <gthelen@google.com> Cc: Michel Lespinasse <walken@google.com> Cc: Rik van Riel <riel@redhat.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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