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Date: Thu, 1 Dec 2022 20:32:53 -0800
From: Mina Almasry <almasrymina@...gle.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Yang Shi <yang.shi@...ux.alibaba.com>,
Yosry Ahmed <yosryahmed@...gle.com>,
Tim Chen <tim.c.chen@...ux.intel.com>, weixugc@...gle.com,
shakeelb@...gle.com, gthelen@...gle.com, fvdl@...gle.com,
Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
Johannes Weiner <hannes@...xchg.org>,
Jonathan Corbet <corbet@....net>,
Michal Hocko <mhocko@...nel.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Muchun Song <songmuchun@...edance.com>,
Andrew Morton <akpm@...ux-foundation.org>,
cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v2] mm: Add nodes= arg to memory.reclaim
On Thu, Dec 1, 2022 at 7:26 PM Huang, Ying <ying.huang@...el.com> wrote:
>
> Mina Almasry <almasrymina@...gle.com> writes:
>
> > The nodes= arg instructs the kernel to only scan the given nodes for
> > proactive reclaim. For example use cases, consider a 2 tier memory system:
> >
> > nodes 0,1 -> top tier
> > nodes 2,3 -> second tier
> >
> > $ echo "1m nodes=0" > memory.reclaim
> >
> > This instructs the kernel to attempt to reclaim 1m memory from node 0.
> > Since node 0 is a top tier node, demotion will be attempted first. This
> > is useful to direct proactive reclaim to specific nodes that are under
> > pressure.
> >
> > $ echo "1m nodes=2,3" > memory.reclaim
> >
> > This instructs the kernel to attempt to reclaim 1m memory in the second tier,
> > since this tier of memory has no demotion targets the memory will be
> > reclaimed.
> >
> > $ echo "1m nodes=0,1" > memory.reclaim
> >
> > Instructs the kernel to reclaim memory from the top tier nodes, which can
> > be desirable according to the userspace policy if there is pressure on
> > the top tiers. Since these nodes have demotion targets, the kernel will
> > attempt demotion first.
> >
> > Since commit 3f1509c57b1b ("Revert "mm/vmscan: never demote for memcg
> > reclaim""), the proactive reclaim interface memory.reclaim does both
> > reclaim and demotion. Reclaim and demotion incur different latency costs
> > to the jobs in the cgroup. Demoted memory would still be addressable
> > by the userspace at a higher latency, but reclaimed memory would need to
> > incur a pagefault.
> >
> > The 'nodes' arg is useful to allow the userspace to control demotion
> > and reclaim independently according to its policy: if the memory.reclaim
> > is called on a node with demotion targets, it will attempt demotion first;
> > if it is called on a node without demotion targets, it will only attempt
> > reclaim.
> >
> > Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> > ---
> > Documentation/admin-guide/cgroup-v2.rst | 15 +++---
> > include/linux/swap.h | 3 +-
> > mm/memcontrol.c | 67 ++++++++++++++++++++-----
> > mm/vmscan.c | 4 +-
> > 4 files changed, 68 insertions(+), 21 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > index 74cec76be9f2..ac5fcbcd5ae6 100644
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -1245,17 +1245,13 @@ PAGE_SIZE multiple when read back.
> > This is a simple interface to trigger memory reclaim in the
> > target cgroup.
> >
> > - This file accepts a single key, the number of bytes to reclaim.
> > - No nested keys are currently supported.
> > + This file accepts a string which contains the number of bytes to
> > + reclaim.
> >
> > Example::
> >
> > echo "1G" > memory.reclaim
> >
> > - The interface can be later extended with nested keys to
> > - configure the reclaim behavior. For example, specify the
> > - type of memory to reclaim from (anon, file, ..).
> > -
> > Please note that the kernel can over or under reclaim from
> > the target cgroup. If less bytes are reclaimed than the
> > specified amount, -EAGAIN is returned.
> > @@ -1267,6 +1263,13 @@ PAGE_SIZE multiple when read back.
> > This means that the networking layer will not adapt based on
> > reclaim induced by memory.reclaim.
> >
> > + This file also allows the user to specify the nodes to reclaim from,
> > + via the 'nodes=' key, example::
> > +
> > + echo "1G nodes=0,1" > memory.reclaim
> > +
> > + The above instructs the kernel to reclaim memory from nodes 0,1.
> > +
> > 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 b61e2007d156..f542c114dffd 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -419,7 +419,8 @@ extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> > extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> > unsigned long nr_pages,
> > gfp_t gfp_mask,
> > - unsigned int reclaim_options);
> > + unsigned int reclaim_options,
> > + nodemask_t nodemask);
> > 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 23750cec0036..a0d7850173a9 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -63,6 +63,7 @@
> > #include <linux/resume_user_mode.h>
> > #include <linux/psi.h>
> > #include <linux/seq_buf.h>
> > +#include <linux/parser.h>
> > #include "internal.h"
> > #include <net/sock.h>
> > #include <net/ip.h>
> > @@ -2392,7 +2393,8 @@ 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,
> > - MEMCG_RECLAIM_MAY_SWAP);
> > + MEMCG_RECLAIM_MAY_SWAP,
> > + NODE_MASK_ALL);
> > psi_memstall_leave(&pflags);
> > } while ((memcg = parent_mem_cgroup(memcg)) &&
> > !mem_cgroup_is_root(memcg));
> > @@ -2683,7 +2685,8 @@ 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, reclaim_options);
> > + gfp_mask, reclaim_options,
> > + NODE_MASK_ALL);
> > psi_memstall_leave(&pflags);
> >
> > if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
> > @@ -3503,7 +3506,8 @@ static int mem_cgroup_resize_max(struct mem_cgroup *memcg,
> > }
> >
> > if (!try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL,
> > - memsw ? 0 : MEMCG_RECLAIM_MAY_SWAP)) {
> > + memsw ? 0 : MEMCG_RECLAIM_MAY_SWAP,
> > + NODE_MASK_ALL)) {
> > ret = -EBUSY;
> > break;
> > }
> > @@ -3614,7 +3618,8 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
> > return -EINTR;
> >
> > if (!try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL,
> > - MEMCG_RECLAIM_MAY_SWAP))
> > + MEMCG_RECLAIM_MAY_SWAP,
> > + NODE_MASK_ALL))
> > nr_retries--;
> > }
> >
> > @@ -6407,7 +6412,8 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
> > }
> >
> > reclaimed = try_to_free_mem_cgroup_pages(memcg, nr_pages - high,
> > - GFP_KERNEL, MEMCG_RECLAIM_MAY_SWAP);
> > + GFP_KERNEL, MEMCG_RECLAIM_MAY_SWAP,
> > + NODE_MASK_ALL);
> >
> > if (!reclaimed && !nr_retries--)
> > break;
> > @@ -6456,7 +6462,8 @@ 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, MEMCG_RECLAIM_MAY_SWAP))
> > + GFP_KERNEL, MEMCG_RECLAIM_MAY_SWAP,
> > + NODE_MASK_ALL))
> > nr_reclaims--;
> > continue;
> > }
> > @@ -6579,21 +6586,54 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
> > return nbytes;
> > }
> >
> > +enum {
> > + MEMORY_RECLAIM_NODES = 0,
> > + MEMORY_RECLAIM_NULL,
> > +};
> > +
> > +static const match_table_t if_tokens = {
> > + { MEMORY_RECLAIM_NODES, "nodes=%s" },
> > + { MEMORY_RECLAIM_NULL, NULL },
> > +};
> > +
> > static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
> > size_t nbytes, loff_t off)
> > {
> > 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;
> > + unsigned int reclaim_options = MEMCG_RECLAIM_MAY_SWAP |
> > + MEMCG_RECLAIM_PROACTIVE;
> > + char *old_buf, *start;
> > + substring_t args[MAX_OPT_ARGS];
> > + int token;
> > + char value[256];
> > + nodemask_t nodemask = NODE_MASK_ALL;
> >
> > buf = strstrip(buf);
> > - err = page_counter_memparse(buf, "", &nr_to_reclaim);
> > - if (err)
> > - return err;
> >
> > - reclaim_options = MEMCG_RECLAIM_MAY_SWAP | MEMCG_RECLAIM_PROACTIVE;
> > + old_buf = buf;
> > + nr_to_reclaim = memparse(buf, &buf) / PAGE_SIZE;
> > + if (buf == old_buf)
> > + return -EINVAL;
> > +
> > + buf = strstrip(buf);
> > +
> > + while ((start = strsep(&buf, " ")) != NULL) {
> > + if (!strlen(start))
> > + continue;
> > + token = match_token(start, if_tokens, args);
> > + match_strlcpy(value, args, sizeof(value));
>
> Per my understanding, we don't need to copy the string, because strsep()
> has replaced " " with "\0". Right?
>
Unless I'm missing something I don't think this has anything to do
with strsep(). `args` is not a null terminated string that can be
passed to nodelist_parse(). Instead it is a struct substring_t that
has args->to and args->from. To convert substring_t args to a null
terminated string, I call match_strlcpy(). I think this is a common
pattern doen in a few places.
I think args->to may point to '\0' because of how strsep() and
match_token() work internally, but I'm somewhat uncomfortable making
assumptions about the implementation of these functions here (it may
change in the future and break the assumption).
> Best Regards,
> Huang, Ying
>
> > + switch (token) {
> > + case MEMORY_RECLAIM_NODES:
> > + if (nodelist_parse(value, nodemask) < 0)
> > + return -EINVAL;
> > + break;
> > + default:
> > + return -EINVAL;
> > + }
> > + }
> > +
> > while (nr_reclaimed < nr_to_reclaim) {
> > unsigned long reclaimed;
> >
> > @@ -6610,7 +6650,8 @@ 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, reclaim_options);
> > + GFP_KERNEL, reclaim_options,
> > + nodemask);
> >
> > if (!reclaimed && !nr_retries--)
> > return -EAGAIN;
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 7b8e8e43806b..23fc5b523764 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -6735,7 +6735,8 @@ 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,
> > - unsigned int reclaim_options)
> > + unsigned int reclaim_options,
> > + nodemask_t nodemask)
> > {
> > unsigned long nr_reclaimed;
> > unsigned int noreclaim_flag;
> > @@ -6750,6 +6751,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> > .may_unmap = 1,
> > .may_swap = !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP),
> > .proactive = !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE),
> > + .nodemask = &nodemask,
> > };
> > /*
> > * Traverse the ZONELIST_FALLBACK zonelist of the current node to put
> > --
> > 2.38.1.584.g0f3c55d4c2-goog
>
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