On Thu 21-07-22 17:30:15, Yosry Ahmed wrote: > memory.reclaim is a cgroup v2 interface that allows users to > proactively reclaim memory from a memcg, without real memory pressure. > Reclaim operations invoke vmpressure, which is used: > (a) To notify userspace of reclaim efficiency in cgroup v1, and > (b) As a signal for a memcg being under memory pressure for networking > (see mem_cgroup_under_socket_pressure()). > > For (a), vmpressure notifications in v1 are not affected by this change > since memory.reclaim is a v2 feature. > > For (b), the effects of the vmpressure signal (according to Shakeel [1]) > are as follows: > 1. Reducing send and receive buffers of the current socket. > 2. May drop packets on the rx path. > 3. May throttle current thread on the tx path. > > Since proactive reclaim is invoked directly by userspace, not by > memory pressure, it makes sense not to throttle networking. Hence, > this change makes sure that proactive reclaim caused by memory.reclaim > does not trigger vmpressure. > > [1] https://lore.kernel.org/lkml/CALvZod68WdrXEmBpOkadhB5GPYmCXaDZzXH=yyGOCAjFRn4NDQ@xxxxxxxxxxxxxx/ > > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> LGTM Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks a lot! > --- > Documentation/admin-guide/cgroup-v2.rst | 7 +++++++ > include/linux/swap.h | 5 ++++- > mm/memcontrol.c | 24 +++++++++++++--------- > mm/vmscan.c | 27 ++++++++++++++++--------- > 4 files changed, 42 insertions(+), 21 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 176298f2f4de..72847462c66d 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1229,6 +1229,13 @@ PAGE_SIZE multiple when read back. > the target cgroup. If less bytes are reclaimed than the > specified amount, -EAGAIN is returned. > > + Please note that the proactive reclaim (triggered by this > + interface) is not meant to indicate memory pressure on the > + memory cgroup. Therefore socket memory balancing triggered by > + the memory reclaim normally is not exercised in this case. > + This means that the networking layer will not adapt based on > + reclaim induced by memory.reclaim. > + > memory.peak > A read-only single value file which exists on non-root > cgroups. > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 0c0fed1b348f..f6e9eaa2339f 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -411,10 +411,13 @@ extern void lru_cache_add_inactive_or_unevictable(struct page *page, > extern unsigned long zone_reclaimable_pages(struct zone *zone); > extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order, > gfp_t gfp_mask, nodemask_t *mask); > + > +#define MEMCG_RECLAIM_MAY_SWAP (1 << 1) > +#define MEMCG_RECLAIM_PROACTIVE (1 << 2) > extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > unsigned long nr_pages, > gfp_t gfp_mask, > - bool may_swap); > + unsigned int reclaim_options); > extern unsigned long mem_cgroup_shrink_node(struct mem_cgroup *mem, > gfp_t gfp_mask, bool noswap, > pg_data_t *pgdat, > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index a550042d88c3..b668224142c7 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2331,7 +2331,8 @@ static unsigned long reclaim_high(struct mem_cgroup *memcg, > > psi_memstall_enter(&pflags); > nr_reclaimed += try_to_free_mem_cgroup_pages(memcg, nr_pages, > - gfp_mask, true); > + gfp_mask, > + MEMCG_RECLAIM_MAY_SWAP); > psi_memstall_leave(&pflags); > } while ((memcg = parent_mem_cgroup(memcg)) && > !mem_cgroup_is_root(memcg)); > @@ -2576,7 +2577,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, > struct page_counter *counter; > unsigned long nr_reclaimed; > bool passed_oom = false; > - bool may_swap = true; > + unsigned int reclaim_options = MEMCG_RECLAIM_MAY_SWAP; > bool drained = false; > unsigned long pflags; > > @@ -2593,7 +2594,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, > mem_over_limit = mem_cgroup_from_counter(counter, memory); > } else { > mem_over_limit = mem_cgroup_from_counter(counter, memsw); > - may_swap = false; > + reclaim_options &= ~MEMCG_RECLAIM_MAY_SWAP; > } > > if (batch > nr_pages) { > @@ -2620,7 +2621,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, > > psi_memstall_enter(&pflags); > nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages, > - gfp_mask, may_swap); > + gfp_mask, reclaim_options); > psi_memstall_leave(&pflags); > > if (mem_cgroup_margin(mem_over_limit) >= nr_pages) > @@ -3402,8 +3403,8 @@ static int mem_cgroup_resize_max(struct mem_cgroup *memcg, > continue; > } > > - if (!try_to_free_mem_cgroup_pages(memcg, 1, > - GFP_KERNEL, !memsw)) { > + if (!try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, > + memsw ? 0 : MEMCG_RECLAIM_MAY_SWAP)) { > ret = -EBUSY; > break; > } > @@ -3513,7 +3514,8 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg) > if (signal_pending(current)) > return -EINTR; > > - if (!try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, true)) > + if (!try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, > + MEMCG_RECLAIM_MAY_SWAP)) > nr_retries--; > } > > @@ -6248,7 +6250,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of, > } > > reclaimed = try_to_free_mem_cgroup_pages(memcg, nr_pages - high, > - GFP_KERNEL, true); > + GFP_KERNEL, MEMCG_RECLAIM_MAY_SWAP); > > if (!reclaimed && !nr_retries--) > break; > @@ -6297,7 +6299,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, > > if (nr_reclaims) { > if (!try_to_free_mem_cgroup_pages(memcg, nr_pages - max, > - GFP_KERNEL, true)) > + GFP_KERNEL, MEMCG_RECLAIM_MAY_SWAP)) > nr_reclaims--; > continue; > } > @@ -6426,6 +6428,7 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf, > struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of)); > unsigned int nr_retries = MAX_RECLAIM_RETRIES; > unsigned long nr_to_reclaim, nr_reclaimed = 0; > + unsigned int reclaim_options; > int err; > > buf = strstrip(buf); > @@ -6433,6 +6436,7 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf, > if (err) > return err; > > + reclaim_options = MEMCG_RECLAIM_MAY_SWAP | MEMCG_RECLAIM_PROACTIVE; > while (nr_reclaimed < nr_to_reclaim) { > unsigned long reclaimed; > > @@ -6449,7 +6453,7 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf, > > reclaimed = try_to_free_mem_cgroup_pages(memcg, > nr_to_reclaim - nr_reclaimed, > - GFP_KERNEL, true); > + GFP_KERNEL, reclaim_options); > > if (!reclaimed && !nr_retries--) > return -EAGAIN; > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f7d9a683e3a7..0969e6408a53 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -102,6 +102,9 @@ struct scan_control { > /* Can pages be swapped as part of reclaim? */ > unsigned int may_swap:1; > > + /* Proactive reclaim invoked by userspace through memory.reclaim */ > + unsigned int proactive:1; > + > /* > * Cgroup memory below memory.low is protected as long as we > * don't threaten to OOM. If any cgroup is reclaimed at > @@ -3125,9 +3128,10 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > sc->priority); > > /* Record the group's reclaim efficiency */ > - vmpressure(sc->gfp_mask, memcg, false, > - sc->nr_scanned - scanned, > - sc->nr_reclaimed - reclaimed); > + if (!sc->proactive) > + vmpressure(sc->gfp_mask, memcg, false, > + sc->nr_scanned - scanned, > + sc->nr_reclaimed - reclaimed); > > } while ((memcg = mem_cgroup_iter(target_memcg, memcg, NULL))); > } > @@ -3250,9 +3254,10 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > } > > /* Record the subtree's reclaim efficiency */ > - vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true, > - sc->nr_scanned - nr_scanned, > - sc->nr_reclaimed - nr_reclaimed); > + if (!sc->proactive) > + vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true, > + sc->nr_scanned - nr_scanned, > + sc->nr_reclaimed - nr_reclaimed); > > if (sc->nr_reclaimed - nr_reclaimed) > reclaimable = true; > @@ -3534,8 +3539,9 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, > __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1); > > do { > - vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup, > - sc->priority); > + if (!sc->proactive) > + vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup, > + sc->priority); > sc->nr_scanned = 0; > shrink_zones(zonelist, sc); > > @@ -3825,7 +3831,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg, > unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > unsigned long nr_pages, > gfp_t gfp_mask, > - bool may_swap) > + unsigned int reclaim_options) > { > unsigned long nr_reclaimed; > unsigned int noreclaim_flag; > @@ -3838,7 +3844,8 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > .priority = DEF_PRIORITY, > .may_writepage = !laptop_mode, > .may_unmap = 1, > - .may_swap = may_swap, > + .may_swap = !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP), > + .proactive = !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE), > }; > /* > * Traverse the ZONELIST_FALLBACK zonelist of the current node to put > -- > 2.37.1.359.gd136c6c3e2-goog -- Michal Hocko SUSE Labs
