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Date: Tue, 29 Nov 2022 11:42:31 -0800
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Shakeel Butt <shakeelb@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...e.com>, Yu Zhao <yuzhao@...gle.com>,
Muchun Song <songmuchun@...edance.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Vasily Averin <vasily.averin@...ux.dev>,
Vlastimil Babka <vbabka@...e.cz>,
Chris Down <chris@...isdown.name>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/3] selftests: cgroup: refactor proactive reclaim code
to reclaim_until()
On Wed, Nov 23, 2022 at 7:16 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> On Wed, Nov 23, 2022 at 5:03 PM Roman Gushchin <roman.gushchin@...ux.dev> wrote:
> >
> > On Wed, Nov 23, 2022 at 09:21:31AM +0000, Yosry Ahmed wrote:
> > > Refactor the code that drives writing to memory.reclaim (retrying, error
> > > handling, etc) from test_memcg_reclaim() to a helper called
> > > reclaim_until(), which proactively reclaims from a memcg until its
> > > usage reaches a certain value.
> > >
> > > This will be used in a following patch in another test.
> > >
> > > Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> > > ---
> > > .../selftests/cgroup/test_memcontrol.c | 85 +++++++++++--------
> > > 1 file changed, 49 insertions(+), 36 deletions(-)
> > >
> > > diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
> > > index 8833359556f3..d4182e94945e 100644
> > > --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> > > +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
> > > @@ -645,6 +645,53 @@ static int test_memcg_max(const char *root)
> > > return ret;
> >
> >
> > The code below looks correct, but can be simplified a bit.
> > And btw thank you for adding a test!
> >
> > Reviewed-by: Roman Gushchin <roman.gushchin@...ux.dev>
> > (idk if you want invest your time in further simplication of this code,
> > it was this way before this patch, so up to you).
>
> I don't "want" to, but the voices in my head won't shut up until I do so..
>
> Here's a patch that simplifies the code, I inlined it here to avoid
> sending a new version. If it looks good to you, it can be squashed
> into this patch or merged separately (whatever you and Andrew prefer).
> I can also send it in a separate thread if preferred.
Roman, any thoughts on this?
>
>
> From 18c40d61dac05b33cfc9233b17979b54422ed7c5 Mon Sep 17 00:00:00 2001
> From: Yosry Ahmed <yosryahmed@...gle.com>
> Date: Thu, 24 Nov 2022 02:21:12 +0000
> Subject: [PATCH] selftests: cgroup: simplify memcg reclaim code
>
> Simplify the code for the reclaim_until() helper used for memcg reclaim
> through memory.reclaim.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
> .../selftests/cgroup/test_memcontrol.c | 65 ++++++++++---------
> 1 file changed, 33 insertions(+), 32 deletions(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c
> b/tools/testing/selftests/cgroup/test_memcontrol.c
> index bac3b91f1579..2e2bde44a6f7 100644
> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
> @@ -17,6 +17,7 @@
> #include <netdb.h>
> #include <errno.h>
> #include <sys/mman.h>
> +#include <limits.h>
>
> #include "../kselftest.h"
> #include "cgroup_util.h"
> @@ -656,51 +657,51 @@ static int test_memcg_max(const char *root)
> return ret;
> }
>
> -/* Reclaim from @memcg until usage reaches @goal_usage */
> +/*
> + * Reclaim from @memcg until usage reaches @goal_usage by writing to
> + * memory.reclaim.
> + *
> + * This function will return false if the usage is already below the
> + * goal.
> + *
> + * This function assumes that writing to memory.reclaim is the only
> + * source of change in memory.current (no concurrent allocations or
> + * reclaim).
> + *
> + * This function makes sure memory.reclaim is sane. It will return
> + * false if memory.reclaim's error codes do not make sense, even if
> + * the usage goal was satisfied.
> + */
> static bool reclaim_until(const char *memcg, long goal_usage)
> {
> char buf[64];
> int retries = 5;
> - int err;
> + int err = INT_MAX;
> long current, to_reclaim;
>
> - /* Nothing to do here */
> - if (cg_read_long(memcg, "memory.current") <= goal_usage)
> - return true;
> -
> while (true) {
> current = cg_read_long(memcg, "memory.current");
> - to_reclaim = current - goal_usage;
>
> - /*
> - * We only keep looping if we get -EAGAIN, which means we could
> - * not reclaim the full amount. This means we got -EAGAIN when
> - * we actually reclaimed the requested amount, so fail.
> - */
> - if (to_reclaim <= 0)
> - break;
> + /* First iteration*/
> + if (err == INT_MAX) {
> + if (current <= goal_usage)
> + return false;
> + /* Write successful, check reclaimed amount */
> + } else if (!err) {
> + return current <= goal_usage ||
> + values_close(current, goal_usage, 3);
> + /* Unexpected error, or ran out of retries */
> + } else if (err != -EAGAIN || !retries--) {
> + return false;
> + /* EAGAIN -> retry, but check for false negatives */
> + } else if (current <= goal_usage) {
> + return false;
> + }
>
> + to_reclaim = current - goal_usage;
> snprintf(buf, sizeof(buf), "%ld", to_reclaim);
> err = cg_write(memcg, "memory.reclaim", buf);
> - if (!err) {
> - /*
> - * If writing succeeds, then the written
> amount should have been
> - * fully reclaimed (and maybe more).
> - */
> - current = cg_read_long(memcg, "memory.current");
> - if (!values_close(current, goal_usage, 3) &&
> current > goal_usage)
> - break;
> - return true;
> - }
> -
> - /* The kernel could not reclaim the full amount, try again. */
> - if (err == -EAGAIN && retries--)
> - continue;
> -
> - /* We got an unexpected error or ran out of retries. */
> - break;
> }
> - return false;
> }
>
> /*
> --
> 2.38.1.584.g0f3c55d4c2-goog
>
> >
> > > }
> > >
> > > +/* Reclaim from @memcg until usage reaches @goal_usage */
> > > +static bool reclaim_until(const char *memcg, long goal_usage)
> > > +{
> > > + char buf[64];
> > > + int retries = 5;
> > > + int err;
> > > + long current, to_reclaim;
> > > +
> > > + /* Nothing to do here */
> > > + if (cg_read_long(memcg, "memory.current") <= goal_usage)
> > > + return true;
> > > +
> > > + while (true) {
> > > + current = cg_read_long(memcg, "memory.current");
> > > + to_reclaim = current - goal_usage;
> > > +
> > > + /*
> > > + * We only keep looping if we get -EAGAIN, which means we could
> > > + * not reclaim the full amount. This means we got -EAGAIN when
> > > + * we actually reclaimed the requested amount, so fail.
> > > + */
> > > + if (to_reclaim <= 0)
> > > + break;
> > > +
> > > + snprintf(buf, sizeof(buf), "%ld", to_reclaim);
> > > + err = cg_write(memcg, "memory.reclaim", buf);
> > > + if (!err) {
> > > + /*
> > > + * If writing succeeds, then the written amount should have been
> > > + * fully reclaimed (and maybe more).
> > > + */
> > > + current = cg_read_long(memcg, "memory.current");
> > > + if (!values_close(current, goal_usage, 3) && current > goal_usage)
> > > + break;
> >
> > There are 3 places in this function where memory.current is read and compared
> > to goal_usage. I believe only one can be left.
> >
> > > + return true;
> > > + }
> > > +
> > > + /* The kernel could not reclaim the full amount, try again. */
> > > + if (err == -EAGAIN && retries--)
> > > + continue;
> > > +
> > > + /* We got an unexpected error or ran out of retries. */
> > > + break;
> >
> > if (err != -EAGAIN || retries--)
> > break;
> >
> > Thanks!
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