linux-kernel - MAP_POPULATE vs. MADV

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Message-ID: <e134e521-54eb-9ae0-f379-26f38703478e@scylladb.com>
Date:   Wed, 15 Mar 2017 18:50:32 +0200
From:   Avi Kivity <avi@...lladb.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: MAP_POPULATE vs. MADV_HUGEPAGES

A user is trying to allocate 1TB of anonymous memory in parallel on 48 
cores (4 NUMA nodes).  The kernel ends up spinning in 
isolate_freepages_block().

I thought to help it along by using MAP_POPULATE, but then my 
MADV_HUGEPAGE won't be seen until after mmap() completes, with pages 
already populated.  Are MAP_POPULATE and MADV_HUGEPAGE mutually exclusive?

Is my only option to serialize those memory allocations, and fault in 
those pages manually?  Or perhaps use mlock()?