Date:   Fri, 1 May 2020 08:38:09 +0200
From:   Guoqing Jiang <guoqing.jiang@...ud.ionos.com>
To:     Andreas Grünbacher <andreas.gruenbacher@...il.com>
Cc:     Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>, willy@...radead.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Yafang Shao <laoar.shao@...il.com>, Song Liu <song@...nel.org>,
        linux-raid@...r.kernel.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Anton Altaparmakov <anton@...era.com>,
        linux-ntfs-dev@...ts.sourceforge.net,
        Mike Marshall <hubcap@...ibond.com>,
        Martin Brandenburg <martin@...ibond.com>,
        devel@...ts.orangefs.org, Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Roman Gushchin <guro@...com>,
        Andreas Dilger <adilger@...ger.ca>
Subject: Re: [RFC PATCH V2 1/9] include/linux/pagemap.h: introduce
 attach/clear_page_private

On 5/1/20 12:10 AM, Andreas Grünbacher wrote:
> Hi,
>
> Am Do., 30. Apr. 2020 um 23:56 Uhr schrieb Guoqing Jiang
> <guoqing.jiang@...ud.ionos.com>:
>> The logic in attach_page_buffers and  __clear_page_buffers are quite
>> paired, but
>>
>> 1. they are located in different files.
>>
>> 2. attach_page_buffers is implemented in buffer_head.h, so it could be
>>     used by other files. But __clear_page_buffers is static function in
>>     buffer.c and other potential users can't call the function, md-bitmap
>>     even copied the function.
>>
>> So, introduce the new attach/clear_page_private to replace them. With
>> the new pair of function, we will remove the usage of attach_page_buffers
>> and  __clear_page_buffers in next patches. Thanks for the new names from
>> Christoph Hellwig.
>>
>> Suggested-by: Matthew Wilcox <willy@...radead.org>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: "Darrick J. Wong" <darrick.wong@...cle.com>
>> Cc: William Kucharski <william.kucharski@...cle.com>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>> Cc: Andreas Gruenbacher <agruenba@...hat.com>
>> Cc: Yang Shi <yang.shi@...ux.alibaba.com>
>> Cc: Yafang Shao <laoar.shao@...il.com>
>> Cc: Song Liu <song@...nel.org>
>> Cc: linux-raid@...r.kernel.org
>> Cc: Chris Mason <clm@...com>
>> Cc: Josef Bacik <josef@...icpanda.com>
>> Cc: David Sterba <dsterba@...e.com>
>> Cc: linux-btrfs@...r.kernel.org
>> Cc: Alexander Viro <viro@...iv.linux.org.uk>
>> Cc: Jaegeuk Kim <jaegeuk@...nel.org>
>> Cc: Chao Yu <chao@...nel.org>
>> Cc: linux-f2fs-devel@...ts.sourceforge.net
>> Cc: Christoph Hellwig <hch@...radead.org>
>> Cc: linux-xfs@...r.kernel.org
>> Cc: Anton Altaparmakov <anton@...era.com>
>> Cc: linux-ntfs-dev@...ts.sourceforge.net
>> Cc: Mike Marshall <hubcap@...ibond.com>
>> Cc: Martin Brandenburg <martin@...ibond.com>
>> Cc: devel@...ts.orangefs.org
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
>> Cc: Roman Gushchin <guro@...com>
>> Cc: Andreas Dilger <adilger@...ger.ca>
>> Signed-off-by: Guoqing Jiang <guoqing.jiang@...ud.ionos.com>
>> ---
>> RFC -> RFC V2:  Address the comments from Christoph Hellwig
>> 1. change function names to attach/clear_page_private and add comments.
>> 2. change the return type of attach_page_private.
>>
>>   include/linux/pagemap.h | 35 +++++++++++++++++++++++++++++++++++
>>   1 file changed, 35 insertions(+)
>>
>> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
>> index a8f7bd8ea1c6..2e515f210b18 100644
>> --- a/include/linux/pagemap.h
>> +++ b/include/linux/pagemap.h
>> @@ -205,6 +205,41 @@ static inline int page_cache_add_speculative(struct page *page, int count)
>>          return __page_cache_add_speculative(page, count);
>>   }
>>
>> +/**
>> + * attach_page_private - attach data to page's private field and set PG_private.
>> + * @page: page to be attached and set flag.
>> + * @data: data to attach to page's private field.
>> + *
>> + * Need to take reference as mm.h said "Setting PG_private should also increment
>> + * the refcount".
>> + */
>> +static inline void attach_page_private(struct page *page, void *data)
>> +{
>> +       get_page(page);
>> +       set_page_private(page, (unsigned long)data);
>> +       SetPagePrivate(page);
>> +}
>> +
>> +/**
>> + * clear_page_private - clear page's private field and PG_private.
>> + * @page: page to be cleared.
>> + *
>> + * The counterpart function of attach_page_private.
>> + * Return: private data of page or NULL if page doesn't have private data.
>> + */
>> +static inline void *clear_page_private(struct page *page)
>> +{
>> +       void *data = (void *)page_private(page);
>> +
>> +       if (!PagePrivate(page))
>> +               return NULL;
>> +       ClearPagePrivate(page);
>> +       set_page_private(page, 0);
>> +       put_page(page);
>> +
>> +       return data;
>> +}
>> +
> I like this in general, but the name clear_page_private suggests that
> this might be the inverse operation of set_page_private, which it is
> not. So maybe this can be renamed to detach_page_private to more
> clearly indicate that it pairs with attach_page_private?

Yes, the new name is better, thank you!

Cheers,
Guoqing

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