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SubjectRe: PATCH: killing read_ahead[]


Alexander Viro wrote:
>
> On Wed, 25 Oct 2000, Jeff V. Merkey wrote:
>
> > Al,
> >
> > Thanks. I'll print this one out and post it on the wall for tonight's
> > debugging session.
> [snip]
> > > (e.g. generic_commit_write have to mess with i_size value to update the
> ^^^^^^^
> Ugh. s/have/doesn't have/, indeed. Sorry.

Wrong syntax:

:%s/have/doesn't have/gc

:-)

>
> As for tonight's debugging session... I love your optimism, but I would
> really like to see comments from Linus. For one thing, patch intersects
> with Rik's one, so I wouldn't expect that to be over tonight (and that's
> completely aside of the chances that Linus will say "no" to that idea).
> Linus?
>
> ObDevices: the last time when we were talking about the devices-in-pagecache
> the things stopped on the ->i_size accesses and related ugliness. IMO the
> main reason of that ugliness was in the attempts to _move_ the i_size to
> address_space. Which was a patently bad idea. How about mirroring it
> there? Notice that atomicity is not an issue - we don't have it when we
> set/modify long long anyway. Said that, I really think that caching the
> values of these expressions makes sense regardless of device handling.

In reality, the file has already been extended in prepare_write() and
the fs's should
always make this assumption. If the write fails, it should be treated
as an I/O error. i_size should be assumed to have been extended at this
point (since the space on the device has
already been allocated.

The way aroud this is to enforce i_size updates in prepare_write()
(this is where I return, "out of space" return codes, and the other FS's
would probably be ok with some minor
changes.).

:-)

Jeff
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