linux-kernel - Re: [PATCH 4/5] mm, swap: Try kzalloc before vzalloc

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Date:   Fri, 17 Mar 2017 01:52:53 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     "Huang, Ying" <ying.huang@...el.com>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Shaohua Li <shli@...nel.org>, Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Aaron Lu <aaron.lu@...el.com>, Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/5] mm, swap: Try kzalloc before vzalloc

On Fri, 17 Mar 2017, Huang, Ying wrote:

> From: Huang Ying <ying.huang@...el.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?