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From:   "Chen, Tim C" <tim.c.chen@intel.com>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Yang Shi <yang.shi@linux.alibaba.com>
CC:     "Huang, Ying" <ying.huang@intel.com>,
        "minchan@kernel.org" <minchan@kernel.org>,
        "daniel.m.jordan@oracle.com" <daniel.m.jordan@oracle.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [v5 PATCH 1/2] mm: swap: check if swap backing device is
 congested or not
Thread-Topic: [v5 PATCH 1/2] mm: swap: check if swap backing device is
 congested or not
Thread-Index: AQHUo5qpOoFpUagMFk+moCKgkvnZWaWpuDWA//96P7A=
Date:   Thu, 10 Jan 2019 23:40:01 +0000
Message-ID: <045D8A5597B93E4EBEDDCBF1FC15F5097E16F8E2@fmsmsx121.amr.corp.intel.com>
References: <1546543673-108536-1-git-send-email-yang.shi@linux.alibaba.com>
 <20190110153147.1baf4c88bf0dd3b8a78aad08@linux-foundation.org>
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> >
> > +	if (si->flags & (SWP_BLKDEV | SWP_FS)) {
> 
> I re-read your discussion with Tim and I must say the reasoning behind this
> test remain foggy.

I was worried that the dereference

inode = si->swap_file->f_mapping->host;

is not always safe for corner cases.

So the test makes sure that the dereference is valid.

> 
> What goes wrong if we just remove it?

If the dereference to get inode is always safe, we can remove it.


Thanks.

Tim