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Date: Fri, 2 Feb 2024 12:48:28 +0800
From: Ming Lei <ming.lei@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	David Hildenbrand <david@redhat.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	Don Dutile <ddutile@redhat.com>, Rafael Aquini <raquini@redhat.com>,
	Dave Chinner <david@fromorbit.com>,
	Mike Snitzer <snitzer@kernel.org>, ming.lei@redhat.com
Subject: Re: [PATCH] mm/madvise: set ra_pages as device max request size
 during ADV_POPULATE_READ
Message-ID: <Zbx0HDYfdneFRs9/@fedora>
References: <20240202022029.1903629-1-ming.lei@redhat.com>
 <Zbxsawh-wlkQ5-8C@casper.infradead.org>
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In-Reply-To: <Zbxsawh-wlkQ5-8C@casper.infradead.org>

On Fri, Feb 02, 2024 at 04:15:39AM +0000, Matthew Wilcox wrote:
> On Fri, Feb 02, 2024 at 10:20:29AM +0800, Ming Lei wrote:
> > +static struct file *madvise_override_ra_win(struct file *f,
> > +		unsigned long start, unsigned long end,
> > +		unsigned int *old_ra_pages)
> > +{
> > +	unsigned int io_pages;
> > +
> > +	if (!f || !f->f_mapping || !f->f_mapping->host)
> > +		return NULL;
> 
> How can ->f_mapping be NULL?  How can f_mapping->host be NULL?

You are right, the two checks can be removed because both two won't
be NULL for opened file, and .f_ra is initialized with
f->f_mapping->host->i_mapping directly too. I will drop the checks
in next version.

BTW, looks the same check in madvise_remove() can removed too.

Thanks,
Ming