linux-kernel - Re: [PATCH][BUG 10227] readahead ret value fix

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Message-ID: <a8e1da0803140408je1f180cra6f6027b39fa07dd@mail.gmail.com>
Date:	Fri, 14 Mar 2008 19:08:14 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	wfg@...l.ustc.edu.cn, akpm@...ux-foundation.org, jack@...e.cz,
	chris@...uxinfotag.de
Subject: Re: [PATCH][BUG 10227] readahead ret value fix

On Fri, Mar 14, 2008 at 6:49 PM, Dave Young <hidave.darkstar@...il.com> wrote:
> If the page_offset > end_index, the return value should be updated to 0,
>  avoiding the redundant read_pages
>
>  Signed-off-by: Dave Young <hidave.darkstar@...il.com>
>
>  ---
>  mm/readahead.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
>  diff -upr linux/mm/readahead.c linux.new/mm/readahead.c
>  --- linux/mm/readahead.c        2008-03-14 18:38:12.000000000 +0800
>  +++ linux.new/mm/readahead.c    2008-03-14 18:38:58.000000000 +0800
>  @@ -144,8 +144,10 @@ __do_page_cache_readahead(struct address
>         for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
>                 pgoff_t page_offset = offset + page_idx;
>
>  -               if (page_offset > end_index)
>  +               if (page_offset > end_index) {
>  +                       ret = 0;
>                         break;
>  +               }
>
>                 rcu_read_lock();
>                 page = radix_tree_lookup(&mapping->page_tree, page_offset);
>

It's not right at all,  sorry for the wrong quick patch.

Anyway, please see the following debug info of me
Mar 14 18:33:51 darkstar kernel: [   19.073085] 3c59x: Donald Becker and others.
Mar 14 18:34:39 darkstar kernel: [  117.837850] #0 page_offset : 0,
end_index : 2 ret: 0
Mar 14 18:34:39 darkstar kernel: [  117.837854] #1 page_offset : 0,
end_index : 2
Mar 14 18:34:39 darkstar kernel: [  117.837861] #0 page_offset : 1,
end_index : 2 ret: 1
Mar 14 18:34:39 darkstar kernel: [  117.837873] #1 page_offset : 1,
end_index : 2
Mar 14 18:34:39 darkstar kernel: [  117.837888] #0 page_offset : 2,
end_index : 2 ret: 2
Mar 14 18:34:39 darkstar kernel: [  117.837911] #1 page_offset : 2,
end_index : 2
Mar 14 18:34:39 darkstar kernel: [  117.837922] #0 page_offset : 3,
end_index : 2 ret: 3
Mar 14 18:34:40 darkstar kernel: [  118.051620] #0 page_offset : 3,
end_index : 2 ret: 0
Mar 14 18:34:40 darkstar kernel: [  118.051626] zisofs : req invalid
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