Minchan,
That sounds good to me.
Thanks,
Wang Sheng-Hui
------------------ Original ------------------
From: "Minchan Kim";<minchan@kernel.org>;
Date: Wed, Jun 1, 2016 03:40 PM
To: "Wang Sheng-Hui"<shhuiw@foxmail.com>;
Cc: "akpm"<akpm@linux-foundation.org>; "mgorman"<mgorman@techsingularity.net>; "iamjoonsoo.kim"<iamjoonsoo.kim@lge.com>; "linux-mm"<linux-mm@kvack.org>; "Vlastimil Babka"<vbabka@suse.cz>;
Subject: Re: Why __alloc_contig_migrate_range calls migrate_prep() at first?
On Wed, Jun 01, 2016 at 11:42:29AM +0800, Wang Sheng-Hui wrote:
> Dear,
>
> Sorry to trouble you.
>
> I noticed cma_alloc would turn to __alloc_contig_migrate_range for allocating pages.
> But __alloc_contig_migrate_range calls migrate_prep() at first, even if the requested page
> is single and free, lru_add_drain_all still run (called by migrate_prep())?
>
> Image a large chunk of free contig pages for CMA, various drivers may request a single page from
> the CMA area, we'll get lru_add_drain_all run for each page.
>
> Should we detect if the required pages are free before migrate_prep(), or detect at least for single
> page allocation?
That makes sense to me.
How about calling migrate_prep once migrate_pages fails in the first trial?
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9d666df5ef95..c504c1a623d2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6623,8 +6623,6 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
unsigned int tries = 0;
int ret = 0;
- migrate_prep();
-
while (pfn < end || !list_empty(&cc->migratepages)) {
if (fatal_signal_pending(current)) {
ret = -EINTR;
@@ -6650,6 +6648,8 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
ret = migrate_pages(&cc->migratepages, alloc_migrate_target,
NULL, 0, cc->mode, MR_CMA);
+if (ret)
+ migrate_prep();
}
if (ret < 0) {
putback_movable_pages(&cc->migratepages);
>
> ------------------
> Regards,
> Wang Sheng-HuiN‹§²æìr¸›zǧu©ž²Æ {†éì¹»®&Þ–)îÆi¢žØ^n‡r¶‰šŽŠÝ¢j$½§$¢¸¢¹¨è§~Š'.)îÄ