linux-kernel - Re: [PATCH] mm: page_alloc: fix the incorrect parameter

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Date: Wed, 15 May 2024 01:50:39 +0000
From: "Yajun Deng" <yajun.deng@...ux.dev>
To: "Johannes Weiner" <hannes@...xchg.org>
Cc: akpm@...ux-foundation.org, vbabka@...e.cz, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: fix the incorrect parameter

May 14, 2024 at 8:40 PM, "Johannes Weiner" <hannes@...xchg.org> wrote:



> 
> On Tue, May 14, 2024 at 02:59:33PM +0800, Yajun Deng wrote:
> 
> > 
> > The first parameter passed to set_pageblock_migratetype should be the
> > 
> >  buddy, not the page. Let's change it back correctly.
> > 
> 
> No it shouldn't be.
> 
> > 
> > Fixes: fd919a85cd55 ("mm: page_isolation: prepare for hygienic freelists")
> > 
> >  Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> > 
> >  ---
> > 
> >  mm/page_alloc.c | 2 +-
> > 
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> >  
> > 
> >  diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > 
> >  index cd584aace6bf..5422f6f8975d 100644
> > 
> >  --- a/mm/page_alloc.c
> > 
> >  +++ b/mm/page_alloc.c
> > 
> >  @@ -1728,7 +1728,7 @@ bool move_freepages_block_isolate(struct zone *zone, struct page *page,
> > 
> >  
> > 
> >  del_page_from_free_list(buddy, zone, order,
> > 
> >  get_pfnblock_migratetype(buddy, pfn));
> > 
> >  - set_pageblock_migratetype(page, migratetype);
> > 
> >  + set_pageblock_migratetype(buddy, migratetype);
> > 
> >  split_large_buddy(zone, buddy, pfn, order);
> > 
> 
> [ pageblock | pageblock ]
> 
> ^ ^
> 
> buddy page
> 
> We're trying to isolate the second pageblock, but it's part of a
> 
> bigger buddy. Remove buddy from the free list, update the migratetype
> 
> of page, then split and free the chunks back. This puts the first
> 
> pageblock back on the original freelist and the second block onto the
> 
> isolate list.
> 
> In the else branch, it's the first block we're interested in:
> 
> [ pageblock | pageblock ]
> 
> ^
> 
> page
> 
> So again, take the whole thing off, but now mark the first block
> 
> isolate, then split and free.
>

Got it, thank you for your detailed explanation.