Re: [PATCH] Use of getblk differs between locations
From: Anton Altaparmakov
Date: Tue Oct 11 2005 - 03:01:59 EST
On Mon, 2005-10-10 at 18:07 -0700, Andrew Morton wrote:
> Mikulas Patocka <mikulas@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > On Mon, 10 Oct 2005, Andrew Morton wrote:
> > > Anton Altaparmakov <aia21@xxxxxxxxx> wrote:
> > >>
> > >> > Maybe the best solution is neither one nor another. Testing and failing
> > >> > gracefully seems better.
> > >> >
> > >> > What do you think?
> > >>
> > >> I certainly agree with you there. I neither want a deadlock nor
> > >> corruption. (-:
> > >
> > > Yup. In the present implementation __getblk_slow() "cannot fail". It's
> > > conceivable that at some future stage we'll change __getblk_slow() so that
> > > it returns NULL on an out-of-memory condition.
> > The question is if it is desired --- it will make bread return NULL on
> > out-of-memory condition, callers will treat it like an IO error, skipping
> > access to the affected block, causing damage on perfectly healthy
> > filesystem.
> Yes, that is a bit dumb. A filesystem might indeed want to take different
> action for ENOMEM versus EIO.
> > I liked what linux-2.0 did in this case --- if the kernel was out of
> > memory, getblk just took another buffer, wrote it if it was dirty and used
> > it. Except for writeable loopback device (where writing one buffer
> > generates more dirty buffers), it couldn't deadlock.
> Wouldn't it be better if bread() were to return ERR_PTR(-EIO) or
> ERR_PTR(-ENOMEM)? Big change.
It would indeed. Much better. And whilst at it, it would be even
better if we had a lot more error codes like "ERR_PTR(-EDEVUNPLUGGED)"
for example... But that would be an even better change. Anyone feeling
like touching every block driver in the kernel? (-;
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/
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