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SubjectRe: [PATCH 03/10] mm, page_alloc: Remove unnecessary recalculations for dirty zone balancing
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On 07/20/2015 10:00 AM, Mel Gorman wrote:
> From: Mel Gorman <mgorman@suse.de>
>
> File-backed pages that will be immediately dirtied are balanced between
> zones but it's unnecessarily expensive. Move consider_zone_balanced into
> the alloc_context instead of checking bitmaps multiple times.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Agreed with new ac->spread_dirty_page name (or rather plural,
spread_dirty_pages?) , and a nitpick below.

> ---
> mm/internal.h | 1 +
> mm/page_alloc.c | 9 ++++++---
> 2 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 36b23f1e2ca6..8977348fbeec 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -129,6 +129,7 @@ struct alloc_context {
> int classzone_idx;
> int migratetype;
> enum zone_type high_zoneidx;
> + bool consider_zone_dirty;
> };
>
> /*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4b35b196aeda..7c2dc022f4ba 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2295,8 +2295,6 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> struct zoneref *z;
> struct page *page = NULL;
> struct zone *zone;
> - bool consider_zone_dirty = (alloc_flags & ALLOC_WMARK_LOW) &&
> - (gfp_mask & __GFP_WRITE);
> int nr_fair_skipped = 0;
> bool zonelist_rescan;
>
> @@ -2355,7 +2353,7 @@ zonelist_scan:

I've been recently suggested by mhocko to add to ~/.gitconfig

[diff "default"]
xfuncname = "^[[:alpha:]$_].*[^:]$"

So that git produces function names in hunk context instead of labels. I
gladly spread this arcane knowledge :)

> * will require awareness of zones in the
> * dirty-throttling and the flusher threads.
> */

This comment (in the part not shown) mentions ALLOC_WMARK_LOW as the
mechanism to distinguish fastpath from slowpath. This is no longer true,
so update it too?

> - if (consider_zone_dirty && !zone_dirty_ok(zone))
> + if (ac->consider_zone_dirty && !zone_dirty_ok(zone))
> continue;
>
> mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
> @@ -2995,6 +2993,10 @@ retry_cpuset:
>
> /* We set it here, as __alloc_pages_slowpath might have changed it */
> ac.zonelist = zonelist;
> +
> + /* Dirty zone balancing only done in the fast path */
> + ac.consider_zone_dirty = (gfp_mask & __GFP_WRITE);
> +
> /* The preferred zone is used for statistics later */
> preferred_zoneref = first_zones_zonelist(ac.zonelist, ac.high_zoneidx,
> ac.nodemask, &ac.preferred_zone);
> @@ -3012,6 +3014,7 @@ retry_cpuset:
> * complete.
> */
> alloc_mask = memalloc_noio_flags(gfp_mask);
> + ac.consider_zone_dirty = false;
>
> page = __alloc_pages_slowpath(alloc_mask, order, &ac);
> }
>



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