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Date: Tue, 25 May 2004 17:14:46 -0700
From: Andrew Morton <akpm@osdl.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: olh@suse.de, linux-kernel@vger.kernel.org
Subject: Re: very low performance on SCSI disks if device node is in tmpfs
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Linus Torvalds <torvalds@osdl.org> wrote:
>
> On Tue, 25 May 2004, Andrew Morton wrote:
> >
> > We need to set file->f_ra _after_ calling blkdev_open(), when inode->i_mapping
> > points at the right thing.  And we need to get it from
> > inode->i_mapping->host->i_mapping too, which represents the underlying device.
> 
> Hmm.. Is f_mapping is guaranteed to be non-NULL?

Yes, we just did

        f->f_mapping = inode->i_mapping;

> At least for the O_DIRECT 
> case, we explicitly test for f_mapping being non-NULL, although that test 
> is quite possibly bogus. Maybe we should fix that too?

yup.