On Thu, 26 Jan 2012 14:59:14 -0500
Rik van Riel <riel@xxxxxxxxxx> wrote:
> When built with CONFIG_COMPACTION, kswapd should not try to free
> contiguous pages, because it is not trying hard enough to have
> a real chance at being successful, but still disrupts the LRU
> enough to break other things.
>
> Do not do higher order page isolation unless we really are in
> lumpy reclaim mode.
>
> Stop reclaiming pages once we have enough free pages that
> compaction can deal with things, and we hit the normal order 0
> watermarks used by kswapd.
>
> Also remove a line of code that increments balanced right before
> exiting the function.
>
> ...
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1139,7 +1139,7 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
> * @mz: The mem_cgroup_zone to pull pages from.
> * @dst: The temp list to put pages on to.
> * @nr_scanned: The number of pages that were scanned.
> - * @order: The caller's attempted allocation order
> + * @sc: The scan_control struct for this reclaim session
> * @mode: One of the LRU isolation modes
> * @active: True [1] if isolating active pages
> * @file: True [1] if isolating file [!anon] pages
> @@ -1148,8 +1148,8 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
> */
> static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> struct mem_cgroup_zone *mz, struct list_head *dst,
> - unsigned long *nr_scanned, int order, isolate_mode_t mode,
> - int active, int file)
> + unsigned long *nr_scanned, struct scan_control *sc,
> + isolate_mode_t mode, int active, int file)
> {
> struct lruvec *lruvec;
> struct list_head *src;
> @@ -1195,7 +1195,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> BUG();
> }
>
> - if (!order)
> + if (!sc->order || !(sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM))
We should have a comment here explaining the reason for the code.
And the immediately following comment isn't very good: "Only take those
pages of the same active state as that tag page". As is common with
poor comments, it tells us "what", but not "why". Reclaiming inactive
_and_ inactive pages would make larger-page freeing more successful and
might be a good thing! Apparently someone felt otherwise, but the
reader is kept in the dark...
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