From: Mel Gorman <mgorman@techsingularity.net>
To: skseofh@gmail.com
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/vmscan.c: no need to double-check if free pages are under high-watermark
Date: Thu, 6 Jan 2022 09:46:50 +0000 [thread overview]
Message-ID: <20220106094650.GX3366@techsingularity.net> (raw)
In-Reply-To: <20220102033129.12913-1-skseofh@gmail.com>
On Sun, Jan 02, 2022 at 12:31:29PM +0900, skseofh@gmail.com wrote:
> From: Daero Lee <skseofh@gmail.com>
>
> In kswapd_try_to_sleep function, to check whether kswapd can sleep,
> the prepare_kswapd_sleep function is called twice.
>
> If free pages are below high-watermark in the first call,
> the @remaining variable is not updated at 0 and the
> prepare_kswapd_sleep function is called for the second time.
>
> I think it is necessary to set the initial value of the
> @remaining to a non-zero value to prevent consecutive calls
> to the same function.
>
> Signed-off-by: Daero Lee <skseofh@gmail.com>
> ---
> mm/vmscan.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 700434db5735..1217ecec5bbb 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4331,7 +4331,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
> /*
> * Return the order kswapd stopped reclaiming at as
> * prepare_kswapd_sleep() takes it into account. If another caller
> - * entered the allocator slow path while kswapd was awake, order will
> + * entered the allqocator slow path while kswapd was awake, order will
> * remain at the higher level.
> */
> return sc.order;
This hunk just adds a typo, drop it.
> @@ -4355,7 +4355,7 @@ static enum zone_type kswapd_highest_zoneidx(pg_data_t *pgdat,
> static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
> unsigned int highest_zoneidx)
> {
> - long remaining = 0;
> + long remaining = ~0;
> DEFINE_WAIT(wait);
>
> if (freezing(current) || kthread_should_stop())
While this does avoid calling prepare_kswapd_sleep() twice if the pgdat
is balanced on the first try, it then does not restore the vmstat
thresholds and doesn't call schedul() for kswapd to go to sleep.
I think you did spot a problem but I suspect you want something like
the following untested patch
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 700434db5735..40784693c840 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4355,7 +4355,8 @@ static enum zone_type kswapd_highest_zoneidx(pg_data_t *pgdat,
static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
unsigned int highest_zoneidx)
{
- long remaining = 0;
+ long remaining;
+ bool balanced;
DEFINE_WAIT(wait);
if (freezing(current) || kthread_should_stop())
@@ -4370,7 +4371,8 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o
* eligible zone balanced that it's also unlikely that compaction will
* succeed.
*/
- if (prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
+ balanced = prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx);
+ if (balanced) {
/*
* Compaction records what page blocks it recently failed to
* isolate pages from and skips them in the future scanning.
@@ -4387,6 +4389,10 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o
remaining = schedule_timeout(HZ/10);
+ /* Is pgdat balanced after a short sleep? */
+ balanced = prepare_kswapd_sleep(pgdat, reclaim_order,
+ highest_zoneidx);
+
/*
* If woken prematurely then reset kswapd_highest_zoneidx and
* order. The values will either be from a wakeup request or
@@ -4406,11 +4412,11 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o
}
/*
- * After a short sleep, check if it was a premature sleep. If not, then
- * go fully to sleep until explicitly woken up.
+ * If balanced to the high watermark, restore vmstat thresholds and
+ * kswapd goes to sleep. If kswapd remains awake, account whether
+ * the low or high watermark was hit quickly.
*/
- if (!remaining &&
- prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
+ if (balanced) {
trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
/*
next prev parent reply other threads:[~2022-01-06 9:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-02 3:31 [PATCH] mm/vmscan.c: no need to double-check if free pages are under high-watermark skseofh
2022-01-06 0:17 ` Andrew Morton
2022-01-06 9:46 ` Mel Gorman [this message]
2022-01-06 12:03 ` DaeRo Lee
2022-01-06 12:57 ` Mel Gorman
2022-03-26 15:50 ` Wei Yang
2022-04-07 13:56 ` Mel Gorman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220106094650.GX3366@techsingularity.net \
--to=mgorman@techsingularity.net \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=skseofh@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).