linux-kernel - Re: [PATCH 05/23] MM: reclaim mustn't enter FS for SWP_FS

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Date:   Sun, 23 Jan 2022 23:31:13 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     NeilBrown <neilb@...e.de>
Cc:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Chuck Lever <chuck.lever@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Christoph Hellwig <hch@...radead.org>,
        David Howells <dhowells@...hat.com>, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/23] MM: reclaim mustn't enter FS for SWP_FS_OPS
 swap-space

On Mon, Jan 24, 2022 at 02:48:32PM +1100, NeilBrown wrote:
> If swap-out is using filesystem operations (SWP_FS_OPS), then it is not
> safe to enter the FS for reclaim.
> So only down-grade the requirement for swap pages to __GFP_IO after
> checking that SWP_FS_OPS are not being used.
> 
> This makes the calculation of "may_enter_fs" slightly more complex, so
> move it into a separate function.  with that done, there is little value
> in maintaining the bool variable any more.  So replace the
> may_enter_fs variable with a may_enter_fs() function.  This removes any
> risk for the variable becoming out-of-date.

Looks good,

Reviewed-by: Christoph Hellwig <hch@....de>