linux-kernel - Re: [PATCH] mm: do not call bad_page on PG

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Message-ID: <Pine.LNX.4.64.0611181326380.6889@blonde.wat.veritas.com>
Date:	Sat, 18 Nov 2006 13:37:53 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	David Rientjes <rientjes@...washington.edu>
cc:	Linus Torvalds <torvalds@...l.org>, Andrew Morton <akpm@...l.org>,
	Andi Kleen <ak@...e.de>, Nick Piggin <npiggin@...e.de>,
	Andre Noll <maan@...temlinux.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: do not call bad_page on PG_reserved check

On Sat, 18 Nov 2006, David Rientjes wrote:

> The return value of free_pages_check() indicates if PG_reserved was set.
> If so, the calling functions return immediately and no pages are freed so
> there is no need to call bad_page().
> 
> Cc: Andi Kleen <ak@...e.de>
> Cc: Nick Piggin <npiggin@...e.de>
> Signed-off-by: David Rientjes <rientjes@...washington.edu>

NAK.  You're missing the point.  If an attempt is made to free a
reserved page, it implies that the page reference counting has
gone wrong: we want to hear about that (so call bad_page),
and we dare not reuse the page (so skip freeing it).

What might be a good change, is to avoid freeing a page which meets
_any_ of the criteria for calling bad_page: I often wonder whether
to do that, alongside abandoning that hopeless page_mapcount BUG in
page_remove_rmap, which has almost(?) never helped lead us to any fix.

Hugh

> ---
>  mm/page_alloc.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bf2f6cf..99bc29d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -439,7 +439,6 @@ static inline int free_pages_check(struc
>  			1 << PG_slab	|
>  			1 << PG_swapcache |
>  			1 << PG_writeback |
> -			1 << PG_reserved |
>  			1 << PG_buddy ))))
>  		bad_page(page);
>  	if (PageDirty(page))
-
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