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

[Minchan Kim <minchan.kim@gmail.com>]

On Thu, Mar 24, 2011 at 12:56 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Thu, 24 Mar 2011 13:55:24 +1100 Stephen Rothwell <sfr@canb.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@canb.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?


-- 
Kind regards,
Minchan Kim