Re: [PATCH V4 1/4] mm: set page->pfmemalloc in prep_new_page()

[Michal Hocko]

On Mon 05-01-15 18:17:40, Vlastimil Babka wrote:
> The function prep_new_page() sets almost everything in the struct page of the
> page being allocated, except page->pfmemalloc. This is not obvious and has at
> least once led to a bug where page->pfmemalloc was forgotten to be set
> correctly, see commit 8fb74b9fb2b1 ("mm: compaction: partially revert capture
> of suitable high-order page").
> 
> This patch moves the pfmemalloc setting to prep_new_page(), which means it
> needs to gain alloc_flags parameter. The call to prep_new_page is moved from
> buffered_rmqueue() to get_page_from_freelist(), which also leads to simpler
> code. An obsolete comment for buffered_rmqueue() is replaced.
> 
> In addition to better maintainability there is a small reduction of code and
> stack usage for get_page_from_freelist(), which inlines the other functions
> involved.
> 
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-145 (-145)
> function                                     old     new   delta
> get_page_from_freelist                      2670    2525    -145
> 
> Stack usage is reduced from 184 to 168 bytes.
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>

get_page_from_freelist has grown too hairy. I agree that it is tiny less
confusing now because we are not breaking out of the loop in the
successful case.

Acked-by: Michal Hocko <mhocko@xxxxxxx>

[...]
> @@ -2177,25 +2181,16 @@ zonelist_scan:
>  try_this_zone:
>  		page = buffered_rmqueue(preferred_zone, zone, order,
>  						gfp_mask, migratetype);
> -		if (page)
> -			break;
> +		if (page) {
> +			if (prep_new_page(page, order, gfp_mask, alloc_flags))
> +				goto try_this_zone;
> +			return page;
> +		}

I would probably liked `do {} while ()' more because it wouldn't use the
goto, but this is up to you:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1bb65e6f48dd..1682d766cb8e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2175,10 +2175,11 @@ zonelist_scan:
 		}
 
 try_this_zone:
-		page = buffered_rmqueue(preferred_zone, zone, order,
+		do {
+			page = buffered_rmqueue(preferred_zone, zone, order,
 						gfp_mask, migratetype);
-		if (page)
-			break;
+		} while (page && prep_new_page(page, order, gfp_mask,
+					       alloc_flags));
 this_zone_full:
 		if (IS_ENABLED(CONFIG_NUMA) && zlc_active)
 			zlc_mark_zone_full(zonelist, z);

[...]
-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/