From: Vlastimil Babka <vbabka@suse.cz>
To: Oscar Salvador <osalvador@suse.de>,
Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-api@vger.kernel.org, hughd@google.com,
kirill@shutemov.name, joel@joelfernandes.org, jglisse@redhat.com,
yang.shi@linux.alibaba.com, mgorman@techsingularity.net
Subject: Re: [PATCH] mm,mremap: Bail out earlier in mremap_to under map pressure
Date: Thu, 28 Feb 2019 09:06:54 +0100 [thread overview]
Message-ID: <5edcfeb8-4f53-0fe6-1e5b-c1e485f91d0d@suse.cz> (raw)
In-Reply-To: <20190227213205.5wdjucqdgfqx33tr@d104.suse.de>
On 2/27/19 10:32 PM, Oscar Salvador wrote:
> On Tue, Feb 26, 2019 at 02:04:28PM -0800, Andrew Morton wrote:
>> How is this going to affect existing userspace which is aware of the
>> current behaviour?
>
> Well, current behavior is not really predictable.
> Our customer was "surprised" that the call to mremap() failed, but the regions
> got unmapped nevertheless.
> They found it the hard way when they got a segfault when trying to write to those
> regions when cleaning up.
>
> As I said in the changelog, the possibility for false positives exists, due to
> the fact that we might get rid of several vma's when unmapping, but I do not
> expect existing userspace applications to start failing.
> Should be that the case, we can revert the patch, it is not that it adds a lot
> of churn.
Hopefully the only program that would start failing would be a LTP test
testing the current behavior near the limit (if such test exists). And
that can be adjusted.
>> And how does it affect your existing cleanup code, come to that? Does
>> it work as well or better after this change?
>
> I guess the customer can trust more reliable that the maps were left untouched.
> I still have my reserves though.
>
> We can get as far as move_vma(), and copy_vma() can fail returning -ENOMEM.
> (Or not due to the "too small to fail" ?)
>
next prev parent reply other threads:[~2019-02-28 8:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-26 9:13 [PATCH] mm,mremap: Bail out earlier in mremap_to under map pressure Oscar Salvador
2019-02-26 22:04 ` Andrew Morton
2019-02-27 21:32 ` Oscar Salvador
2019-02-28 8:06 ` Vlastimil Babka [this message]
2019-02-28 20:44 ` Joel Fernandes
2019-03-01 15:25 ` Cyril Hrubis
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