Date: Fri, 17 Mar 2017 01:52:53 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
To: "Huang, Ying" <ying.huang@intel.com>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Shaohua Li <shli@kernel.org>, Rik van Riel <riel@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        =?UTF-8?Q?J=C3=A9r=C3=B4me_Glisse?= <jglisse@redhat.com>,
        Aaron Lu <aaron.lu@intel.com>, Hugh Dickins <hughd@google.com>,
        Minchan Kim <minchan@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Vegard Nossum <vegard.nossum@oracle.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 4/5] mm, swap: Try kzalloc before vzalloc
In-Reply-To: <20170317064635.12792-4-ying.huang@intel.com>
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References: <20170317064635.12792-1-ying.huang@intel.com> <20170317064635.12792-4-ying.huang@intel.com>
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On Fri, 17 Mar 2017, Huang, Ying wrote:

> From: Huang Ying <ying.huang@intel.com>
> 
> Now vzalloc() is used in swap code to allocate various data
> structures, such as swap cache, swap slots cache, cluster info, etc.
> Because the size may be too large on some system, so that normal
> kzalloc() may fail.  But using kzalloc() has some advantages, for
> example, less memory fragmentation, less TLB pressure, etc.  So change
> the data structure allocation in swap code to try to use kzalloc()
> firstly, and fallback to vzalloc() if kzalloc() failed.
> 

I'm concerned about preferring kzalloc() with __GFP_RECLAIM since the page 
allocator will try to do memory compaction for high-order allocations when 
the vzalloc() would have succeeded immediately.  Do we necessarily want to 
spend time doing memory compaction and direct reclaim for contiguous 
memory if it's not needed?