linux-kernel - Re: [PATCH] mm: page_alloc: dump migrate-failed pages only at -EBUSY

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Date:   Thu, 20 May 2021 12:19:55 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: page_alloc: dump migrate-failed pages only at -EBUSY

On Wed, May 19, 2021 at 02:33:41PM -0700, Minchan Kim wrote:
> alloc_contig_dump_pages aims for helping debugging page migration
> failure by page refcount mismatch or something else of page itself
> from migration handler function. However, in -ENOMEM case, there is
> nothing to get clue from page descriptor information so just
> dump pages only when -EBUSY happens.
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  mm/page_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3100fcb08500..c0a2971dc755 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8760,7 +8760,8 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
>  
>  	lru_cache_enable();
>  	if (ret < 0) {
> -		alloc_contig_dump_pages(&cc->migratepages);
> +		if (ret == -EBUSY)
> +			alloc_contig_dump_pages(&cc->migratepages);
>  		putback_movable_pages(&cc->migratepages);
>  		return ret;
>  	}
> -- 
> 2.31.1.751.gd2f1c929bd-goog
> 

Resend with a little modifying description.

>From c5a2fea291cf46079b87cc9ac9a25fc7f819d0fd Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@...nel.org>
Date: Wed, 19 May 2021 14:22:18 -0700
Subject: [PATCH] mm: page_alloc: dump migrate-failed pages only at -EBUSY

alloc_contig_dump_pages aims for helping debugging page migration
failure by elevated page refcount compared to expected_count.
(for the detail, please look at migrate_page_move_mapping)

However, -ENOMEM is just the case that system is under memory
pressure state, not relevant with page refcount at all. Thus,
the dumping page list is not helpful for the debugging point of view.

Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 mm/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3100fcb08500..c0a2971dc755 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8760,7 +8760,8 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 
 	lru_cache_enable();
 	if (ret < 0) {
-		alloc_contig_dump_pages(&cc->migratepages);
+		if (ret == -EBUSY)
+			alloc_contig_dump_pages(&cc->migratepages);
 		putback_movable_pages(&cc->migratepages);
 		return ret;
 	}
-- 
2.31.1.818.g46aad6cb9e-goog