linux-kernel - Re: linux-next: manual merge of the cleancache tree with Linus' tree

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Message-ID: <AANLkTimQQHHN6pS17R_mGmF+oG33D3Apb6E_pNvsLHwv@mail.gmail.com>
Date:	Thu, 24 Mar 2011 14:58:06 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus <torvalds@...ux-foundation.org>
Subject: Re: linux-next: manual merge of the cleancache tree with Linus' tree

On Thu, Mar 24, 2011 at 2:38 PM, Minchan Kim <minchan.kim@...il.com> wrote:
> On Thu, Mar 24, 2011 at 12:56 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
>> On Thu, 24 Mar 2011 13:55:24 +1100 Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>>
>>> Hi Dan,
>>>
>>> Today's linux-next merge of the cleancache tree got a conflict in
>>> mm/truncate.c between commit 5adc7b518b54 ("mm: truncate: change
>>> remove_from_page_cache") from Linus' tree and commit 03e838947c8a
>>> ("mm/fs: add hooks to support cleancache") from the cleancache tree.
>>>
>>> I fixed it up (see below) but am really not sure of the fix.  I can carry
>>> this fix as necessary.
>>>
>>> Is this stuff going to be merged into Linus' tree this time round?
>>> --
>>> Cheers,
>>> Stephen Rothwell                    sfr@...b.auug.org.au
>>>
>>> diff --cc mm/truncate.c
>>> index a956675,cd94607..0000000
>>> --- a/mm/truncate.c
>>> +++ b/mm/truncate.c
>>> @@@ -106,8 -108,13 +108,12 @@@ truncate_complete_page(struct address_s
>>>       cancel_dirty_page(page, PAGE_CACHE_SIZE);
>>>
>>>       clear_page_mlock(page);
>>>  -    remove_from_page_cache(page);
>>>       ClearPageMappedToDisk(page);
>>>  +    delete_from_page_cache(page);
>>> +     /* this must be after the remove_from_page_cache which
>>> +      * calls cleancache_put_page (and note page->mapping is now NULL)
>>> +      */
>>> +     cleancache_flush_page(mapping, page);
>>>  -    page_cache_release(page);       /* pagecache ref */
>>>       return 0;
>>>   }
>>
>> I did the cleancache_flush_page() before the delete_from_page_cache(),
>> in case the delete_from_page_cache() freed the page.  I didn't actually
>> check whether that makes sense though.
>
> I am not sure cleancache's put and flush semantic.
> If I understand rightly with old __remove_from_page_cache's comment,
> maybe cleancache_flush_page is to invalidate the page.(If I understand
> right, I hope the name is changed to cleancache_invalidate_page)
>
> "        /*
>         * if we're uptodate, flush out into the cleancache, otherwise
>         * invalidate any existing cleancache entries.  We can't leave
>         * stale data around in the cleancache once our page is gone
>         */
>        if (PageUptodate(page))
>                cleancache_put_page(page);
>        else
>                cleancache_flush_page(mapping, page); "
>
> So I think cleancache_flush_page should be done after
> delete_from_page_cache because delete_from_page_cache calls
> cleancache_put_page(maybe this function would flush the content of
> memory into cleancache's target) before we invalidates the page.
>
> And it should not be a problem in case the delete_from_page_cache
> freed the page since cleancache should have a reference the page but I
> didn't check cleancahe always has a reference of page. If it isn't,
> it's a critical problem.
>
> Dan, Could you comment this?

Dan, one more thing.

#define cleancache_fs_enabled_mapping(_mapping) \
        (mapping->host->i_sb->cleancache_poolid >= 0)

One is "_mapping", another is  "mapping"


-- 
Kind regards,
Minchan Kim
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