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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 24/27] libxfs: add a buftarg cache shrinker implementation
Date: Thu, 15 Oct 2020 11:01:41 -0700
Message-ID: <20201015180141.GZ9832@magnolia> (raw)
In-Reply-To: <20201015072155.1631135-25-david@fromorbit.com>

On Thu, Oct 15, 2020 at 06:21:52PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Add a list_lru scanner that runs from the memory pressure detection
> to free an amount of the buffer cache that will keep the cache from
> growing when there is memory pressure.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  libxfs/buftarg.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
> 
> diff --git a/libxfs/buftarg.c b/libxfs/buftarg.c
> index 6c7142d41eb1..8332bf3341b6 100644
> --- a/libxfs/buftarg.c
> +++ b/libxfs/buftarg.c
> @@ -62,6 +62,19 @@ xfs_buftarg_setsize_early(
>  	return xfs_buftarg_setsize(btp, bsize);
>  }
>  
> +static void
> +dispose_list(
> +	struct list_head	*dispose)
> +{
> +	struct xfs_buf		*bp;
> +
> +	while (!list_empty(dispose)) {
> +		bp = list_first_entry(dispose, struct xfs_buf, b_lru);
> +		list_del_init(&bp->b_lru);
> +		xfs_buf_rele(bp);
> +	}
> +}
> +
>  /*
>   * Scan a chunk of the buffer cache and drop LRU reference counts. If the
>   * count goes to zero, dispose of the buffer.
> @@ -70,6 +83,13 @@ static void
>  xfs_buftarg_shrink(
>  	struct xfs_buftarg	*btc)
>  {
> +	struct list_lru		*lru = &btc->bt_lru;
> +	struct xfs_buf		*bp;
> +	int			count;
> +	int			progress = 16384;
> +	int			rotate = 0;
> +	LIST_HEAD(dispose);
> +
>  	/*
>  	 * Make the fact we are in memory reclaim externally visible. This
>  	 * allows buffer cache allocation throttling while we are trying to
> @@ -79,6 +99,37 @@ xfs_buftarg_shrink(
>  
>  	fprintf(stderr, "Got memory pressure event. Shrinking caches!\n");
>  
> +	spin_lock(&lru->l_lock);
> +	count = lru->l_count / 50;	/* 2% */

If I'm reading this correctly, we react to a memory pressure event by
trying to skim 2% of the oldest disposable buffers off the buftarg LRU?
And every 16384 loop iterations we'll dispose the list even if we
haven't gotten our 2% yet?  How did you arrive at 2%?

(Also, I'm assuming that some of these stderr printfs will at some point
get turned into tracepoints or dbg_printf or the like?)

--D

> +	fprintf(stderr, "cache size before %ld/%d\n", lru->l_count, count);
> +	while (count-- > 0 && !list_empty(&lru->l_lru)) {
> +		bp = list_first_entry(&lru->l_lru, struct xfs_buf, b_lru);
> +		spin_lock(&bp->b_lock);
> +		if (!atomic_add_unless(&bp->b_lru_ref, -1, 1)) {
> +			atomic_set(&bp->b_lru_ref, 0);
> +			bp->b_state |= XFS_BSTATE_DISPOSE;
> +			list_move(&bp->b_lru, &dispose);
> +			lru->l_count--;
> +		} else {
> +			rotate++;
> +			list_move_tail(&bp->b_lru, &lru->l_lru);
> +		}
> +
> +		spin_unlock(&bp->b_lock);
> +		if (--progress == 0) {
> +			fprintf(stderr, "Disposing! rotated %d, lru %ld\n", rotate, lru->l_count);
> +			spin_unlock(&lru->l_lock);
> +			dispose_list(&dispose);
> +			spin_lock(&lru->l_lock);
> +			progress = 16384;
> +			rotate = 0;
> +		}
> +	}
> +	spin_unlock(&lru->l_lock);
> +
> +	dispose_list(&dispose);
> +	fprintf(stderr, "cache size after %ld, count remaining %d\n", lru->l_count, count);
> +
>  	/*
>  	 * Now we've free a bunch of memory, trim the heap down to release the
>  	 * freed memory back to the kernel and reduce the pressure we are
> -- 
> 2.28.0
> 

  reply index

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-15  7:21 [PATCH 00/27] [RFC, WIP] xfsprogs: xfs_buf unification and AIO Dave Chinner
2020-10-15  7:21 ` [PATCH 01/27] xfsprogs: remove unused buffer tracing code Dave Chinner
2020-10-15  7:21 ` [PATCH 02/27] xfsprogs: remove unused IO_DEBUG functionality Dave Chinner
2020-11-16  2:31   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 03/27] libxfs: get rid of b_bcount from xfs_buf Dave Chinner
2020-11-23 19:53   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 04/27] libxfs: rename buftarg->dev to btdev Dave Chinner
2020-11-16  2:33   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 05/27] xfsprogs: get rid of ancient btree tracing fragments Dave Chinner
2020-11-16  2:35   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 06/27] xfsprogs: remove xfs_buf_t typedef Dave Chinner
2020-10-15 15:22   ` Darrick J. Wong
2020-10-15 20:54     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 07/27] xfsprogs: introduce liburcu support Dave Chinner
2020-10-15  7:21 ` [PATCH 08/27] libxfs: add spinlock_t wrapper Dave Chinner
2020-10-15  7:21 ` [PATCH 09/27] atomic: convert to uatomic Dave Chinner
2020-10-15  7:21 ` [PATCH 10/27] libxfs: add kernel-compatible completion API Dave Chinner
2020-10-15 17:09   ` Darrick J. Wong
2020-10-19 22:21     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 11/27] libxfs: add wrappers for kernel semaphores Dave Chinner
2020-10-15  7:21 ` [PATCH 12/27] xfsprogs: convert use-once buffer reads to uncached IO Dave Chinner
2020-10-15 17:12   ` Darrick J. Wong
2020-10-19 22:36     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 13/27] libxfs: introduce userspace buftarg infrastructure Dave Chinner
2020-10-15  7:21 ` [PATCH 14/27] xfs: rename libxfs_buftarg_init to libxfs_open_devices() Dave Chinner
2020-10-15  7:21 ` [PATCH 15/27] libxfs: introduce userspace buftarg infrastructure Dave Chinner
2020-10-15 17:16   ` Darrick J. Wong
2020-10-15  7:21 ` [PATCH 16/27] libxfs: add a synchronous IO engine to the buftarg Dave Chinner
2020-10-15  7:21 ` [PATCH 17/27] xfsprogs: convert libxfs_readbufr to libxfs_buf_read_uncached Dave Chinner
2020-10-15  7:21 ` [PATCH 18/27] libxfs: convert libxfs_bwrite to buftarg IO Dave Chinner
2020-10-15  7:21 ` [PATCH 19/27] libxfs: add cache infrastructure to buftarg Dave Chinner
2020-10-15  7:21 ` [PATCH 20/27] libxfs: add internal lru to btcache Dave Chinner
2020-10-15  7:21 ` [PATCH 21/27] libxfs: Add kernel list_lru wrapper Dave Chinner
2020-10-15  7:21 ` [PATCH 22/27] libxfs: introduce new buffer cache infrastructure Dave Chinner
2020-10-15 17:46   ` Darrick J. Wong
2020-10-15  7:21 ` [PATCH 23/27] libxfs: use PSI information to detect memory pressure Dave Chinner
2020-10-15 17:56   ` Darrick J. Wong
2020-10-15 21:20     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 24/27] libxfs: add a buftarg cache shrinker implementation Dave Chinner
2020-10-15 18:01   ` Darrick J. Wong [this message]
2020-10-15 21:33     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 25/27] libxfs: switch buffer cache implementations Dave Chinner
2020-10-15  7:21 ` [PATCH 26/27] build: set platform_defs.h.in dependency correctly Dave Chinner
2020-10-15  7:21 ` [PATCH 27/27] libxfs: convert sync IO buftarg engine to AIO Dave Chinner
2020-10-15 18:26   ` Darrick J. Wong
2020-10-15 21:42     ` Dave Chinner
2020-10-15  7:29 ` [PATCH 00/27] [RFC, WIP] xfsprogs: xfs_buf unification and AIO Dave Chinner
2020-10-15 18:37 ` Darrick J. Wong
2020-10-15 22:35   ` Dave Chinner

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