Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with cpuset update

From: Christoph Lameter <cl@linux.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	cgroups@vger.kernel.org, Li Zefan <lizefan@huawei.com>,
	Michal Hocko <mhocko@kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	David Rientjes <rientjes@google.com>,
	Hugh Dickins <hughd@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with cpuset update
Date: Tue, 11 Apr 2017 12:24:25 -0500 (CDT)	[thread overview]
Message-ID: <alpine.DEB.2.20.1704111152170.25069@east.gentwo.org> (raw)
In-Reply-To: <20170411140609.3787-2-vbabka@suse.cz>

On Tue, 11 Apr 2017, Vlastimil Babka wrote:

> The root of the problem is that the cpuset's mems_allowed and mempolicy's
> nodemask can temporarily have no intersection, thus get_page_from_freelist()
> cannot find any usable zone. The current semantic for empty intersection is to
> ignore mempolicy's nodemask and honour cpuset restrictions. This is checked in
> node_zonelist(), but the racy update can happen after we already passed the

The fallback was only intended for a cpuset on which boundaries are not enforced
in critical conditions (softwall). A hardwall cpuset (CS_MEM_HARDWALL)
should fail the allocation.

> This patch fixes the issue by having __alloc_pages_slowpath() check for empty
> intersection of cpuset and ac->nodemask before OOM or allocation failure. If
> it's indeed empty, the nodemask is ignored and allocation retried, which mimics
> node_zonelist(). This works fine, because almost all callers of

Well that would need to be subject to the hardwall flag. Allocation needs
to fail for a hardwall cpuset.