linux-kernel - Re: [git pull] common helper for kmap_local

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Date:   Sat, 11 Mar 2023 18:11:01 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [git pull] common helper for kmap_local_page() users in local filesystems

On venerdì 10 marzo 2023 21:44:31 CET Al Viro wrote:
> 	kmap_local_page() conversions in local filesystems keep running into
> kunmap_local_page()+put_page() combinations; we can keep inventing names
> for identical inline helpers, but it's getting rather inconvenient.  I've
> added a trivial helper to linux/highmem.h instead.

Yeah, "put_and_unmap_page()". Nice helper :-)

Today I decided to prepare a series to convert all the functions of all the 
filesystems where I had found the above-mentioned pattern but I stopped 
immediately after converting dir_put_page() in fs/sysv.

Why? Just because I realized that I do not understand the reasons behind the 
choice of the name of the helper...  

Why did you name it "put_and_unmap_page()" instead of "unmap_and_put_page()", 
for we always unmap first _and_ put the page immediately the unmapping?

It seems it want to imply that instead we put first and unmap later (which 
would be wrong). That name sounds misleading to me and not sound (logically 
speaking).

Am I missing some obscure convention behind your choice of that name for the 
helper?

If not, can you please change it from "put_and_unmap_page()" to 
"unmap_and_put_page()"? 

Thanks,

Fabio

> 
> 	I would've held that back until the merge window, if not for the
> mess it causes in tree topology - I've several branches merging from that
> one, and it's only going to get worse if e.g. ext2 stuff gets picked by
> Jan.
> 
> 	The helper is trivial and it's early in the cycle.  It would 
simplify
> the things if you could pull it - then I'd simply rebase the affected 
branches
> to -rc2...
> 
> The following changes since commit fe15c26ee26efa11741a7b632e9f23b01aca4cc6:
> 
>   Linux 6.3-rc1 (2023-03-05 14:52:03 -0800)
> 
> are available in the Git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git tags/pull-
highmem
> 
> for you to fetch changes up to 849ad04cf562ac63b0371a825eed473d84de9c6d:
> 
>   new helper: put_and_unmap_page() (2023-03-07 01:50:53 -0500)
> 
> ----------------------------------------------------------------
> put_and_unmap_page() helper
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> 
> ----------------------------------------------------------------
> Al Viro (1):
>       new helper: put_and_unmap_page()
> 
>  include/linux/highmem.h | 6 ++++++
>  1 file changed, 6 insertions(+)