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Date: Mon, 25 Jul 2022 09:27:15 +0200
From: Michal Hocko <mhocko@...e.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Shakeel Butt <shakeelb@...gle.com>,
Muchun Song <songmuchun@...edance.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
Vlastimil Babka <vbabka@...e.cz>,
David Hildenbrand <david@...hat.com>,
Miaohe Lin <linmiaohe@...wei.com>, NeilBrown <neilb@...e.de>,
Alistair Popple <apopple@...dia.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5] mm: vmpressure: don't count proactive reclaim in
vmpressure
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@mail.gmail.com/
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
LGTM
Acked-by: Michal Hocko <mhocko@...e.com>
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
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