(2013/04/09 20:06), Mel Gorman wrote:
> Simplistically, the anon and file LRU lists are scanned proportionally
> depending on the value of vm.swappiness although there are other factors
> taken into account by get_scan_count(). The patch "mm: vmscan: Limit
> the number of pages kswapd reclaims" limits the number of pages kswapd
> reclaims but it breaks this proportional scanning and may evenly shrink
> anon/file LRUs regardless of vm.swappiness.
>
> This patch preserves the proportional scanning and reclaim. It does mean
> that kswapd will reclaim more than requested but the number of pages will
> be related to the high watermark.
>
> [mho...@suse.cz: Correct proportional reclaim for memcg and simplify]
> Signed-off-by: Mel Gorman <mgor...@suse.de>
> Acked-by: Rik van Riel <r...@redhat.com>
> ---
> mm/vmscan.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 46 insertions(+), 8 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 4835a7a..0742c45 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1825,13 +1825,21 @@ static void shrink_lruvec(struct lruvec *lruvec,
> struct scan_control *sc)
> enum lru_list lru;
> unsigned long nr_reclaimed = 0;
> unsigned long nr_to_reclaim = sc->nr_to_reclaim;
> + unsigned long nr_anon_scantarget, nr_file_scantarget;
> struct blk_plug plug;
> + bool scan_adjusted = false;
>
> get_scan_count(lruvec, sc, nr);
>
> + /* Record the original scan target for proportional adjustments later */
> + nr_file_scantarget = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE] + 1;
> + nr_anon_scantarget = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON] + 1;
> +
I'm sorry I couldn't understand the calc...
Assume here
nr_file_scantarget = 100
nr_anon_file_target = 100.
> blk_start_plug(&plug);
> while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
> nr[LRU_INACTIVE_FILE]) {
> + unsigned long nr_anon, nr_file, percentage;
> +
> for_each_evictable_lru(lru) {
> if (nr[lru]) {
> nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
> @@ -1841,17 +1849,47 @@ static void shrink_lruvec(struct lruvec *lruvec,
> struct scan_control *sc)
> lruvec, sc);
> }
> }
> +
> + if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
> + continue;
> +
> /*
> - * On large memory systems, scan >> priority can become
> - * really large. This is fine for the starting priority;
> - * we want to put equal scanning pressure on each zone.
> - * However, if the VM has a harder time of freeing pages,
> - * with multiple processes reclaiming pages, the total
> - * freeing target can get unreasonably large.
> + * For global direct reclaim, reclaim only the number of pages
> + * requested. Less care is taken to scan proportionally as it
> + * is more important to minimise direct reclaim stall latency
> + * than it is to properly age the LRU lists.
> */
> - if (nr_reclaimed >= nr_to_reclaim &&
> - sc->priority < DEF_PRIORITY)
> + if (global_reclaim(sc) && !current_is_kswapd())
> break;
> +
> + /*
> + * For kswapd and memcg, reclaim at least the number of pages
> + * requested. Ensure that the anon and file LRUs shrink
> + * proportionally what was requested by get_scan_count(). We
> + * stop reclaiming one LRU and reduce the amount scanning
> + * proportional to the original scan target.
> + */
> + nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
> + nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
> +
Then, nr_file = 80, nr_anon=70.
> + if (nr_file > nr_anon) {
> + lru = LRU_BASE;
> + percentage = nr_anon * 100 / nr_anon_scantarget;
> + } else {
> + lru = LRU_FILE;
> + percentage = nr_file * 100 / nr_file_scantarget;
> + }
the percentage will be 70.
> +
> + /* Stop scanning the smaller of the LRU */
> + nr[lru] = 0;
> + nr[lru + LRU_ACTIVE] = 0;
> +
this will stop anon scan.
> + /* Reduce scanning of the other LRU proportionally */
> + lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
> + nr[lru] = nr[lru] * percentage / 100;;
> + nr[lru + LRU_ACTIVE] = nr[lru + LRU_ACTIVE] * percentage / 100;
> +
finally, in the next iteration,
nr[file] = 80 * 0.7 = 56.
After loop, anon-scan is 30 pages , file-scan is 76(20+56) pages..
I think the calc here should be
nr[lru] = nr_lru_scantarget * percentage / 100 - nr[lru]
Here, 80-70=10 more pages to scan..should be proportional.
Am I misunderstanding ?
Thanks,
-Kame
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