From: Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH 2/8] xfs: abstract PF_FSTRANS to PF_MEMALLOC_NOFS
Date: Mon, 9 Jan 2017 13:59:05 +0100
Message-ID: <bf7594a9-7e1a-0895-2d0e-df1f27502db1@suse.cz>
References: <20170106141107.23953-1-mhocko@kernel.org>
 <20170106141107.23953-3-mhocko@kernel.org>
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Cc: Andrew Morton <akpm@linux-foundation.org>,
 Dave Chinner <david@fromorbit.com>, djwong@kernel.org,
 Theodore Ts'o <tytso@mit.edu>, Chris Mason <clm@fb.com>,
 David Sterba <dsterba@suse.cz>, Jan Kara <jack@suse.cz>,
 ceph-devel@vger.kernel.org, cluster-devel@redhat.com,
 linux-nfs@vger.kernel.org, logfs@logfs.org, linux-xfs@vger.kernel.org,
 linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org,
 linux-mtd@lists.infradead.org, reiserfs-devel@vger.kernel.org,
 linux-ntfs-dev@lists.sourceforge.net,
 linux-f2fs-devel@lists.sourceforge.net, linux-afs@lists.infradead.org,
 LKML <linux-kernel@vger.kernel.org>, Michal Hocko <mhocko@suse.com>
To: Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org,
 linux-fsdevel@vger.kernel.org
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In-Reply-To: <20170106141107.23953-3-mhocko@kernel.org>
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On 01/06/2017 03:11 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> xfs has defined PF_FSTRANS to declare a scope GFP_NOFS semantic quite
> some time ago. We would like to make this concept more generic and use
> it for other filesystems as well. Let's start by giving the flag a
> more generic name PF_MEMALLOC_NOFS which is in line with an exiting
> PF_MEMALLOC_NOIO already used for the same purpose for GFP_NOIO
> contexts. Replace all PF_FSTRANS usage from the xfs code in the first
> step before we introduce a full API for it as xfs uses the flag directly
> anyway.
> 
> This patch doesn't introduce any functional change.
> 
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: Brian Foster <bfoster@redhat.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

A nit:

> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2320,6 +2320,8 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut,
>  #define PF_FREEZER_SKIP	0x40000000	/* Freezer should not count it as freezable */
>  #define PF_SUSPEND_TASK 0x80000000      /* this thread called freeze_processes and should not be frozen */
>  
> +#define PF_MEMALLOC_NOFS PF_FSTRANS	/* Transition to a more generic GFP_NOFS scope semantic */

I don't see why this transition is needed, as there are already no users
of PF_FSTRANS after this patch. The next patch doesn't remove any more,
so this is just extra churn IMHO. But not a strong objection.

> +
>  /*
>   * Only the _current_ task can read/write to tsk->flags, but other
>   * tasks can access tsk->flags in readonly mode for example
> 

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