From: Dave Chinner <david@fromorbit.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 0/5] export __clear_page_buffers to cleanup code
Date: Mon, 20 Apr 2020 09:20:46 +1000 [thread overview]
Message-ID: <20200419232046.GC9765@dread.disaster.area> (raw)
In-Reply-To: <20200419031443.GT5820@bombadil.infradead.org>
On Sat, Apr 18, 2020 at 08:14:43PM -0700, Matthew Wilcox wrote:
> On Sun, Apr 19, 2020 at 12:51:18AM +0200, Guoqing Jiang wrote:
> > When reading md code, I find md-bitmap.c copies __clear_page_buffers from
> > buffer.c, and after more search, seems there are some places in fs could
> > use this function directly. So this patchset tries to export the function
> > and use it to cleanup code.
>
> OK, I see why you did this, but there are a couple of problems with it.
>
> One is just a sequencing problem; between exporting __clear_page_buffers()
> and removing it from the md code, the md code won't build.
>
> More seriously, most of this code has nothing to do with buffers. It
> uses page->private for its own purposes.
>
> What I would do instead is add:
>
> clear_page_private(struct page *page)
> {
> ClearPagePrivate(page);
> set_page_private(page, 0);
> put_page(page);
> }
>
> to include/linux/mm.h, then convert all callers of __clear_page_buffers()
> to call that instead.
While I think this is the right direction, I don't like the lack of
symmetry between set_page_private() and clear_page_private() this
creates. i.e. set_page_private() just assigned page->private, while
clear_page_private clears both a page flag and page->private, and it
also drops a page reference, too.
Anyone expecting to use set/clear_page_private as a matched pair (as
the names suggest they are) is in for a horrible surprise...
This is a public service message brought to you by the Department
of We Really Suck At API Design.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2020-04-19 23:20 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-18 22:51 [PATCH 0/5] export __clear_page_buffers to cleanup code Guoqing Jiang
2020-04-18 22:51 ` [PATCH 1/5] fs/buffer: export __clear_page_buffers Guoqing Jiang
2020-04-19 7:56 ` Nikolay Borisov
2020-04-19 13:20 ` Guoqing Jiang
2020-04-18 22:51 ` [PATCH 2/5] btrfs: call __clear_page_buffers to simplify code Guoqing Jiang
2020-04-19 19:46 ` David Sterba
2020-04-19 20:32 ` Guoqing Jiang
2020-04-18 22:51 ` [PATCH 3/5] iomap: call __clear_page_buffers in iomap_page_release Guoqing Jiang
2020-04-19 7:47 ` Christoph Hellwig
2020-04-19 13:18 ` Guoqing Jiang
2020-04-18 22:51 ` [RFC PATCH 4/5] orangefs: call __clear_page_buffers to simplify code Guoqing Jiang
2020-04-18 22:51 ` [PATCH 5/5] md-bitmap: don't duplicate code for __clear_page_buffers Guoqing Jiang
2020-04-19 3:14 ` [PATCH 0/5] export __clear_page_buffers to cleanup code Matthew Wilcox
2020-04-19 5:14 ` Gao Xiang
2020-04-19 13:22 ` Guoqing Jiang
2020-04-19 13:15 ` Guoqing Jiang
2020-04-19 20:31 ` Guoqing Jiang
2020-04-19 21:17 ` Matthew Wilcox
2020-04-19 23:20 ` Dave Chinner [this message]
2020-04-20 0:30 ` Matthew Wilcox
2020-04-20 21:14 ` Guoqing Jiang
2020-04-20 22:14 ` Matthew Wilcox
2020-04-21 1:53 ` Dave Chinner
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