From: Brian Foster <bfoster@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 11/28] mm: factor shrinker work calculations
Date: Mon, 4 Nov 2019 10:29:39 -0500 [thread overview]
Message-ID: <20191104152939.GB10665@bfoster> (raw)
In-Reply-To: <20191031234618.15403-12-david@fromorbit.com>
On Fri, Nov 01, 2019 at 10:46:01AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Start to clean up the shrinker code by factoring out the calculation
> that determines how much work to do. This separates the calculation
> from clamping and other adjustments that are done before the
> shrinker work is run. Document the scan batch size calculation
> better while we are there.
>
> Also convert the calculation for the amount of work to be done to
> use 64 bit logic so we don't have to keep jumping through hoops to
> keep calculations within 32 bits on 32 bit systems.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
I assume the kbuild warning thing will be fixed up...
> mm/vmscan.c | 97 ++++++++++++++++++++++++++++++++++++++---------------
> 1 file changed, 70 insertions(+), 27 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a215d71d9d4b..2d39ec37c04d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -459,13 +459,68 @@ EXPORT_SYMBOL(unregister_shrinker);
>
> #define SHRINK_BATCH 128
>
> +/*
> + * Calculate the number of new objects to scan this time around. Return
> + * the work to be done. If there are freeable objects, return that number in
> + * @freeable_objects.
> + */
> +static int64_t shrink_scan_count(struct shrink_control *shrinkctl,
> + struct shrinker *shrinker, int priority,
> + int64_t *freeable_objects)
> +{
> + int64_t delta;
> + int64_t freeable;
> +
> + freeable = shrinker->count_objects(shrinker, shrinkctl);
> + if (freeable == 0 || freeable == SHRINK_EMPTY)
> + return freeable;
> +
> + if (shrinker->seeks) {
> + /*
> + * shrinker->seeks is a measure of how much IO is required to
> + * reinstantiate the object in memory. The default value is 2
> + * which is typical for a cold inode requiring a directory read
> + * and an inode read to re-instantiate.
> + *
> + * The scan batch size is defined by the shrinker priority, but
> + * to be able to bias the reclaim we increase the default batch
> + * size by 4. Hence we end up with a scan batch multipler that
> + * scales like so:
> + *
> + * ->seeks scan batch multiplier
> + * 1 4.00x
> + * 2 2.00x
> + * 3 1.33x
> + * 4 1.00x
> + * 8 0.50x
> + *
> + * IOWs, the more seeks it takes to pull the item into cache,
> + * the smaller the reclaim scan batch. Hence we put more reclaim
> + * pressure on caches that are fast to repopulate and to keep a
> + * rough balance between caches that have different costs.
> + */
> + delta = freeable >> (priority - 2);
Does anything prevent priority < 2 here?
> + do_div(delta, shrinker->seeks);
> + } else {
> + /*
> + * These objects don't require any IO to create. Trim them
> + * aggressively under memory pressure to keep them from causing
> + * refetches in the IO caches.
> + */
> + delta = freeable / 2;
> + }
> +
> + *freeable_objects = freeable;
> + return delta > 0 ? delta : 0;
> +}
> +
> static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> struct shrinker *shrinker, int priority)
> {
> unsigned long freed = 0;
> - unsigned long long delta;
> long total_scan;
> - long freeable;
> + int64_t freeable_objects = 0;
> + int64_t scan_count;
> long nr;
> long new_nr;
> int nid = shrinkctl->nid;
...
> @@ -487,25 +543,11 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> */
> nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
>
> - total_scan = nr;
> - if (shrinker->seeks) {
> - delta = freeable >> priority;
> - delta *= 4;
> - do_div(delta, shrinker->seeks);
> - } else {
> - /*
> - * These objects don't require any IO to create. Trim
> - * them aggressively under memory pressure to keep
> - * them from causing refetches in the IO caches.
> - */
> - delta = freeable / 2;
> - }
> -
> - total_scan += delta;
> + total_scan = nr + scan_count;
> if (total_scan < 0) {
> pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n",
> shrinker->scan_objects, total_scan);
> - total_scan = freeable;
> + total_scan = scan_count;
Same question as before: why the change in assignment? freeable was the
->count_objects() return value, which is now stored in freeable_objects.
FWIW, the change seems to make sense in that it just factors out the
deferred count, but it's not clear if it's intentional...
Brian
> next_deferred = nr;
> } else
> next_deferred = total_scan;
> @@ -522,19 +564,20 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> * Hence only allow the shrinker to scan the entire cache when
> * a large delta change is calculated directly.
> */
> - if (delta < freeable / 4)
> - total_scan = min(total_scan, freeable / 2);
> + if (scan_count < freeable_objects / 4)
> + total_scan = min_t(long, total_scan, freeable_objects / 2);
>
> /*
> * Avoid risking looping forever due to too large nr value:
> * never try to free more than twice the estimate number of
> * freeable entries.
> */
> - if (total_scan > freeable * 2)
> - total_scan = freeable * 2;
> + if (total_scan > freeable_objects * 2)
> + total_scan = freeable_objects * 2;
>
> trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
> - freeable, delta, total_scan, priority);
> + freeable_objects, scan_count,
> + total_scan, priority);
>
> /*
> * If the shrinker can't run (e.g. due to gfp_mask constraints), then
> @@ -559,7 +602,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> * possible.
> */
> while (total_scan >= batch_size ||
> - total_scan >= freeable) {
> + total_scan >= freeable_objects) {
> unsigned long ret;
> unsigned long nr_to_scan = min(batch_size, total_scan);
>
> --
> 2.24.0.rc0
>
next prev parent reply other threads:[~2019-11-04 15:29 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-31 23:45 [PATCH 00/28] mm, xfs: non-blocking inode reclaim Dave Chinner
2019-10-31 23:45 ` [PATCH 01/28] xfs: Lower CIL flush limit for large logs Dave Chinner
2019-10-31 23:45 ` [PATCH 02/28] xfs: Throttle commits on delayed background CIL push Dave Chinner
2019-11-01 12:04 ` Brian Foster
2019-11-01 21:40 ` Dave Chinner
2019-11-04 22:48 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 03/28] xfs: don't allow log IO to be throttled Dave Chinner
2019-10-31 23:45 ` [PATCH 04/28] xfs: Improve metadata buffer reclaim accountability Dave Chinner
2019-11-01 12:05 ` Brian Foster
2019-11-04 23:21 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 05/28] xfs: correctly acount for reclaimable slabs Dave Chinner
2019-10-31 23:45 ` [PATCH 06/28] xfs: factor common AIL item deletion code Dave Chinner
2019-11-04 23:16 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 07/28] xfs: tail updates only need to occur when LSN changes Dave Chinner
2019-11-04 23:18 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 08/28] xfs: factor inode lookup from xfs_ifree_cluster Dave Chinner
2019-11-01 12:05 ` Brian Foster
2019-11-04 23:20 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 09/28] mm: directed shrinker work deferral Dave Chinner
2019-11-04 15:25 ` Brian Foster
2019-11-14 20:49 ` Dave Chinner
2019-11-15 17:21 ` Brian Foster
2019-11-18 0:49 ` Dave Chinner
2019-11-19 15:12 ` Brian Foster
2019-10-31 23:46 ` [PATCH 10/28] shrinkers: use defer_work for GFP_NOFS sensitive shrinkers Dave Chinner
2019-10-31 23:46 ` [PATCH 11/28] mm: factor shrinker work calculations Dave Chinner
2019-11-02 10:55 ` kbuild test robot
2019-11-04 15:29 ` Brian Foster [this message]
2019-11-14 20:59 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 12/28] shrinker: defer work only to kswapd Dave Chinner
2019-11-04 15:29 ` Brian Foster
2019-11-14 21:11 ` Dave Chinner
2019-11-15 17:23 ` Brian Foster
2019-10-31 23:46 ` [PATCH 13/28] shrinker: clean up variable types and tracepoints Dave Chinner
2019-11-04 15:30 ` Brian Foster
2019-10-31 23:46 ` [PATCH 14/28] mm: reclaim_state records pages reclaimed, not slabs Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-10-31 23:46 ` [PATCH 15/28] mm: back off direct reclaim on excessive shrinker deferral Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-11-14 21:28 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 16/28] mm: kswapd backoff for shrinkers Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-11-14 21:41 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 17/28] xfs: synchronous AIL pushing Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 18/28] xfs: don't block kswapd in inode reclaim Dave Chinner
2019-10-31 23:46 ` [PATCH 19/28] xfs: reduce kswapd blocking on inode locking Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 20/28] xfs: kill background reclaim work Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 21/28] xfs: use AIL pushing for inode reclaim IO Dave Chinner
2019-11-05 17:06 ` Brian Foster
2019-10-31 23:46 ` [PATCH 22/28] xfs: remove mode from xfs_reclaim_inodes() Dave Chinner
2019-10-31 23:46 ` [PATCH 23/28] xfs: track reclaimable inodes using a LRU list Dave Chinner
2019-10-31 23:46 ` [PATCH 24/28] xfs: reclaim inodes from the LRU Dave Chinner
2019-11-06 17:21 ` Brian Foster
2019-11-14 21:51 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 25/28] xfs: remove unusued old inode reclaim code Dave Chinner
2019-11-06 17:21 ` Brian Foster
2019-10-31 23:46 ` [PATCH 26/28] xfs: use xfs_ail_push_all in xfs_reclaim_inodes Dave Chinner
2019-11-06 17:22 ` Brian Foster
2019-11-14 21:53 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 27/28] rwsem: introduce down/up_write_non_owner Dave Chinner
2019-10-31 23:46 ` [PATCH 28/28] xfs: rework unreferenced inode lookups Dave Chinner
2019-11-06 22:18 ` Brian Foster
2019-11-14 22:16 ` Dave Chinner
2019-11-15 13:13 ` Christoph Hellwig
2019-11-15 17:26 ` Brian Foster
2019-11-18 1:00 ` Dave Chinner
2019-11-19 15:13 ` Brian Foster
2019-11-19 21:18 ` Dave Chinner
2019-11-20 12:42 ` Brian Foster
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