linux-kernel - Re: [PATCH] vfs: does call expand

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Date:	Wed, 18 Nov 2009 16:35:13 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Liu Aleaxander <aleaxander@...il.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] vfs: does call expand_files when needed

On Wed, Nov 18, 2009 at 3:41 PM, Liu Aleaxander <aleaxander@...il.com> wrote:
> On Wed, Nov 18, 2009 at 3:17 PM, Américo Wang <xiyou.wangcong@...il.com> wrote:
>>
>> On Wed, Nov 18, 2009 at 1:54 PM, Liu Aleaxander <aleaxander@...il.com> wrote:
>> > From: Liu Aleaxander <Aleaxander@...il.com>
>> > Date: Wed, 18 Nov 2009 10:59:09 +0800
>> > Subject: [PATCH] vfs: does call expand_files when needed
>> >
>> > I don't think we should call expand_files every time we open a
>> > file for a new unused fd, so does the expand when necessary.
>> >
>> > Signed-off-by: Liu Aleaxander <Aleaxander@...il.com>
>> > ---
>> >  fs/file.c |   27 ++++++++++++++-------------
>> >  1 files changed, 14 insertions(+), 13 deletions(-)
>> >
>> > diff --git a/fs/file.c b/fs/file.c
>> > index 87e1290..3f3d0fc 100644
>> > --- a/fs/file.c
>> > +++ b/fs/file.c
>> > @@ -452,22 +452,22 @@ repeat:
>> >        if (fd < files->next_fd)
>> >                fd = files->next_fd;
>> >
>> > -       if (fd < fdt->max_fds)
>> > +       if (likely(fd < fdt->max_fds)) {
>> >                fd = find_next_zero_bit(fdt->open_fds->fds_bits,
>> >                                           fdt->max_fds, fd);
>> > -
>> > -       error = expand_files(files, fd);
>> > -       if (error < 0)
>> > -               goto out;
>> > -
>> > -       /*
>> > -        * If we needed to expand the fs array we
>> > -        * might have blocked - try again.
>> > -        */
>> > -       if (error)
>> > -               goto repeat;
>> > -
>> > +       } else {
>> > +               error = expand_files(files, fd);
>>
>>
>> In expand_files(), it has the check for
>> ' < fdt->max_fds', so this change is not necessary.
>
> Yeah, indeed. But why we should go into an another function to do a
> _double_ check especially we mostly don't need to do that?

You only optimized one call path, it's trivial, not so much an
improvement, IMO.
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