linux-kernel - RE: [EXTERNAL] [PATCH v3 05/12] cifs: drop usage of page_file

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Message-ID:
 <MW4PR21MB18900803310D7D7887554BE3E41A2@MW4PR21MB1890.namprd21.prod.outlook.com>
Date: Tue, 30 Apr 2024 02:23:03 +0000
From: Steven French <Steven.French@...rosoft.com>
To: Matthew Wilcox <willy@...radead.org>
CC: Kairui Song <kasong@...cent.com>, "linux-mm@...ck.org"
	<linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, "Huang,
 Ying" <ying.huang@...el.com>, Chris Li <chrisl@...nel.org>, Barry Song
	<v-songbaohua@...o.com>, Ryan Roberts <ryan.roberts@....com>, Neil Brown
	<neilb@...e.de>, Minchan Kim <minchan@...nel.org>, Hugh Dickins
	<hughd@...gle.com>, David Hildenbrand <david@...hat.com>, Yosry Ahmed
	<yosryahmed@...gle.com>, "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Namjae Jeon <linkinjeon@...nel.org>, "Paulo
 Alcantara (SUSE)" <pc@...guebit.com>, Shyam Prasad
	<Shyam.Prasad@...rosoft.com>, Bharath S M <bharathsm@...rosoft.com>
Subject: RE: [EXTERNAL] [PATCH v3 05/12] cifs: drop usage of page_file_offset

Makes sense - I will try to look at this fixing the swapon and reading from swap over smb3.1.1 mounts in the next few weeks, but if you have a good example of sample code (from one of the other FS that does this well) that would help.

-----Original Message-----
From: Matthew Wilcox <willy@...radead.org> 
Sent: Monday, April 29, 2024 3:26 PM
To: Steven French <Steven.French@...rosoft.com>
Cc: Kairui Song <kasong@...cent.com>; linux-mm@...ck.org; Andrew Morton <akpm@...ux-foundation.org>; Huang, Ying <ying.huang@...el.com>; Chris Li <chrisl@...nel.org>; Barry Song <v-songbaohua@...o.com>; Ryan Roberts <ryan.roberts@....com>; Neil Brown <neilb@...e.de>; Minchan Kim <minchan@...nel.org>; Hugh Dickins <hughd@...gle.com>; David Hildenbrand <david@...hat.com>; Yosry Ahmed <yosryahmed@...gle.com>; linux-fsdevel@...r.kernel.org; linux-kernel@...r.kernel.org; Namjae Jeon <linkinjeon@...nel.org>; Paulo Alcantara (SUSE) <pc@...guebit.com>; Shyam Prasad <Shyam.Prasad@...rosoft.com>; Bharath S M <bharathsm@...rosoft.com>
Subject: Re: [EXTERNAL] [PATCH v3 05/12] cifs: drop usage of page_file_offset

On Mon, Apr 29, 2024 at 08:19:31PM +0000, Steven French wrote:
> Wouldn't this make it harder to fix the regression when swap file support was temporarily removed from cifs.ko (due to the folio migration)?   I was hoping to come back to fixing swapfile support for cifs.ko in 6.10-rc (which used to pass the various xfstests for this but code got removed with folios/netfs changes).

It was neither the folio conversion nor the netfs conversion which removed the claim of swap support from cifs, but NeilBrown's introduction of ->swap_rw.  In commit e1209d3a7a67 he claims that

    Only two filesystems set SWP_FS_OPS:
    - cifs sets the flag, but ->direct_IO always fails so swap cannot work.
    - nfs sets the flag, but ->direct_IO calls generic_write_checks()
      which has failed on swap files for several releases.

As I recall the xfstests only checked that swapon/swapoff works; they don't actually test that writing to swap and reading back from it work.