linux-kernel - Re: [PATCH 8/8] readahead: dont do start-of-file readahead after lseek()

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Message-ID: <20111122141829.GB29261@localhost>
Date:	Tue, 22 Nov 2011 22:18:29 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 8/8] readahead: dont do start-of-file readahead after
 lseek()

> > --- linux-next.orig/fs/read_write.c	2011-11-20 22:02:01.000000000 +0800
> > +++ linux-next/fs/read_write.c	2011-11-20 22:02:03.000000000 +0800
> > @@ -47,6 +47,10 @@ static loff_t lseek_execute(struct file 
> >  		file->f_pos = offset;
> >  		file->f_version = 0;
> >  	}
> > +
> > +	if (!(file->f_ra.ra_flags & READAHEAD_LSEEK))
> > +		file->f_ra.ra_flags |= READAHEAD_LSEEK;
> > +
> >  	return offset;
> >  }
> 
> Confused.  How does READAHEAD_LSEEK get cleared again?

I thought it's not necessary (at least for this case). But yeah, it's
good to clear it to make it more reasonable and avoid unexpected things.

And it would be simple to do, in ra_submit():

-       ra->ra_flags &= ~READAHEAD_MMAP;
+       ra->ra_flags &= ~(READAHEAD_MMAP | READAHEAD_LSEEK);

Thanks,
Fengguang
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