Re: Checking page_count(page) in invalidate_complete_page

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andrew Morton wrote:

>On Wed, 27 Sep 2006 14:47:26 +1000
>Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>
>>truncate_inode_pages will a) throw away everything including dirty 
>>pages, and b) probably be fairly
>>racy unless the inode's i_size (for normal files) is modified.
>>
>>We really want to make an invalidation that works properly for you.
>>
>>If you can guarantee that a pagecache page can never get mapped to a 
>>user mapping (eg. perhaps for
>>directories and symlinks) and also ensure that you don't dirty it via 
>>the filesystem, then you don't
>>have to worry about it becoming dirty, so we can skip the checks Andrew 
>>has added and maybe add a
>>WARN_ON(PageDirty()).
>>
>
>None of that is true for when invalidate_inode_pages2() is used by
>block-backed direct-io.
>

Sure, you wouldn't be able to skip those checks for direct IO, just for the
NFS usage.

>We should fix it for that application..
>

I thought direct IO fell back to buffered IO when the teardown failed. I
was surprised that it didn't and gave me errors when I was testing. Do
you see a better way to handle the direct IO case?

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