linux-ext4 - Re: [PATCH 2/3] buffer: Hoist GFP flags from grow_dev_page() to __getblk

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Message-ID: <ZQNCHeUAtpP9EFNX@casper.infradead.org>
Date:   Thu, 14 Sep 2023 18:25:49 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Jan Kara <jack@...e.cz>
Cc:     akpm@...ux-foundation.org, Hui Zhu <teawater@...group.com>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/3] buffer: Hoist GFP flags from grow_dev_page() to
 __getblk_gfp()

On Thu, Sep 14, 2023 at 11:16:25AM +0200, Jan Kara wrote:
> On Fri 11-08-23 17:15:27, Matthew Wilcox (Oracle) wrote:
> > grow_dev_page() is only called by grow_buffers().  grow_buffers()
> > is only called by __getblk_slow() and __getblk_slow() is only called
> > from __getblk_gfp(), so it is safe to move the GFP flags setting
> > all the way up.  With that done, add a new bdev_getblk() entry point
> > that leaves the GFP flags the way the caller specified them.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> 
> Can't we just finish this gfp parameter conversion for all the users?
> There are five __getblk_gfp() users, three in buffer_head.h directly
> generate gfp mask, two (__bread_gfp() and sb_getblk_gfp()) pass it from the
> caller. All three __bread_gfp() callers are in buffer_head.h and directly
> generate gfp mask. sb_getblk_gfp() has five callers, all in ext4 and easily
> convertable as well.
> 
> This results not only in cleaner code but also just checking
> sb_getblk_gfp() callers shows how confused they currently are about the gfp
> argument (passing NOFS, NOFAIL and other pointless flags). Secondly, we can
> keep using sb_getblk_gfp() from the filesystems instead of having to decide
> between sb_getblk_gfp() and bdev_getblk().

I didn't do __bread_gfp() because it's basically an internal interface.
All users call sb_bread(), sb_bread_unmovable() or __bread().
It doesn't seem worth doing.  Now, if we start to see people actually
using __bread_gfp() outside of those three interfaces, I'd agree we need
to make it use GFP flags properly.

BTW, Andrew has taken the bdev_getblk() series into the mm tree, so
testing that tree might be a good idea for the ext4 developers (and other
filesystems; an earlier revision of this patchset  had a bug which would
have only affected nilfs2).