linux-kernel - Re: [PATCH 1/2] mm: page_alloc: speed up fallbacks in rmqueue

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Message-ID: <20250409140023.GA2313@cmpxchg.org>
Date: Wed, 9 Apr 2025 10:00:23 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Yunsheng Lin <linyunsheng@...wei.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Brendan Jackman <jackmanb@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Carlos Song <carlos.song@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel test robot <oliver.sang@...el.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: page_alloc: speed up fallbacks in rmqueue_bulk()

On Wed, Apr 09, 2025 at 04:02:39PM +0800, Yunsheng Lin wrote:
> On 2025/4/8 2:01, Johannes Weiner wrote:
> > @@ -2934,6 +2981,7 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
> >  {
> >  	struct page *page;
> >  	unsigned long flags;
> > +	enum rmqueue_mode rmqm = RMQUEUE_NORMAL;
> >  
> >  	do {
> >  		page = NULL;
> > @@ -2945,7 +2993,7 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
> >  		if (alloc_flags & ALLOC_HIGHATOMIC)
> >  			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
> >  		if (!page) {
> > -			page = __rmqueue(zone, order, migratetype, alloc_flags);
> > +			page = __rmqueue(zone, order, migratetype, alloc_flags, &rmqm);
> >  
> >  			/*
> >  			 * If the allocation fails, allow OOM handling and
> 
> It was not in the diff, but it seems the zone->lock is held inside the do..while loop,
> doesn't it mean that the freelists are subject to outside changes and rmqm is stale?

Yes. Note that it only loops when there is a bug/corrupted page, so it
won't make much difference in practice. But it's still kind of weird.

Thanks for your review, Yunsheng!

Andrew, could you please fold the below fixlet?

---

>From 71b1eea7ded41c1f674909f9755c23b9ee9bcb6a Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@...xchg.org>
Date: Wed, 9 Apr 2025 09:56:52 -0400
Subject: [PATCH] mm: page_alloc: speed up fallbacks in rmqueue_bulk() fix

reset rmqueue_mode in rmqueue_buddy() error loop, per Yunsheng Lin

Signed-off-by: Johannes Weiner <hannes@...xchg.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 dfb2b3f508af..7ffeeb0f62d3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2983,7 +2983,6 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
 {
 	struct page *page;
 	unsigned long flags;
-	enum rmqueue_mode rmqm = RMQUEUE_NORMAL;
 
 	do {
 		page = NULL;
@@ -2996,6 +2995,8 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
 		if (alloc_flags & ALLOC_HIGHATOMIC)
 			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
 		if (!page) {
+			enum rmqueue_mode rmqm = RMQUEUE_NORMAL;
+
 			page = __rmqueue(zone, order, migratetype, alloc_flags, &rmqm);
 
 			/*
-- 
2.49.0