Re: [rfc] lockless pagecache

Nick Piggin
2005-06-27T09:04:14Z

Lincoln Dale wrote:
> Nick Piggin wrote:
> [..]
>
>> However I think for Oracle and others that use shared memory like
>> this, they are probably not doing linear access, so that would be a
>> net loss. I'm not completely sure (I don't have access to real loads
>> at the moment), but I would have thought those guys would have looked
>> into fault ahead if it were a possibility.
>
>
> i thought those guys used O_DIRECT - in which case, wouldn't the page
> cache not be used?
>

Well I think they do use O_DIRECT for their IO, but they need to
use the Linux pagecache for their shared memory - that shared
memory being the basis for their page cache. I think. Whatever
the setup I believe they have issues with the tree_lock, which is
why it was changed to an rwlock.

--
SUSE Labs, Novell Inc.

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