linux-kernel - Re: [PATCH v12 7/9] hugetlb: support file

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Date:   Sat, 15 Feb 2020 17:29:59 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Mina Almasry <almasrymina@...gle.com>
cc:     mike.kravetz@...cle.com, shuah@...nel.org, shakeelb@...gle.com,
        gthelen@...gle.com, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v12 7/9] hugetlb: support file_region coalescing again

On Tue, 11 Feb 2020, Mina Almasry wrote:

> An earlier patch in this series disabled file_region coalescing in order
> to hang the hugetlb_cgroup uncharge info on the file_region entries.
> 
> This patch re-adds support for coalescing of file_region entries.
> Essentially everytime we add an entry, we call a recursive function that
> tries to coalesce the added region with the regions next to it. The
> worst case call depth for this function is 3: one to coalesce with the
> region next to it, one to coalesce to the region prev, and one to reach
> the base case.
> 
> This is an important performance optimization as private mappings add
> their entries page by page, and we could incur big performance costs for
> large mappings with lots of file_region entries in their resv_map.
> 
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>

Acked-by: David Rientjes <rientjes@...gle.com>