Re: [PATCH] osd fs: __r4w_get_page rely on PageUptodate for uptodate

From: Boaz Harrosh
Date: Mon Nov 02 2015 - 06:05:44 EST

On 11/02/2015 01:39 AM, Hugh Dickins wrote:
>> This patch is not correct!
> I think you have actually confirmed that the patch is correct:
> why bother to test PageDirty or PageWriteback when PageUptodate
> already tells you what you need?
> Or do these filesystems do something unusual with PageUptodate
> when PageDirty is set? I didn't find it.

This is kind of delicate stuff. It took me a while to get it right
when I did it. I don't remember all the details.

But consider this option:

exofs_write_begin on a full PAGE_CACHE_SIZE, the page is instantiated
new in page-cache is that PageUptodate(page) then? I thought not.
(exofs does not set that)

Now that page I do not want to read in. The latest data is in memory.
(Same when this page is in writeback, dirty-bit is cleared)

So for sure if page is dirty or writeback then we surly do not need a read.
only if not then we need to consider the PageUptodate(page) state.

Do you think the code is actually wrong as is?

BTW: Very similar code is in fs/nfs/objlayout/objio_osd.c::__r4w_get_page

> Thanks,
> Hugh


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