linux-kernel - Re: [RFC v2 PATCH 0/4] speed up page allocation for __GFP

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Message-ID: <87wnx9rcjq.fsf@oracle.com>
Date:   Tue, 22 Dec 2020 12:11:21 -0500
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Liang Li <liliang.opensource@...il.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        Liang Li <liliangleo@...iglobal.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [RFC v2 PATCH 0/4] speed up page allocation for __GFP_ZERO

Liang Li <liliang.opensource@...il.com> writes:
> The first version can be found at: https://lkml.org/lkml/2020/4/12/42
>
> Zero out the page content usually happens when allocating pages with
> the flag of __GFP_ZERO, this is a time consuming operation, it makes
> the population of a large vma area very slowly. This patch introduce
> a new feature for zero out pages before page allocation, it can help
> to speed up page allocation with __GFP_ZERO.

kzeropaged appears to escape some of the kernel's resource controls, at
least if I'm understanding this right.

The heavy part of a page fault is moved out of the faulting task's
context so the CPU controller can't throttle it.  A task that uses
these pages can benefit from clearing done by CPUs that it's not allowed
to run on.  How can it handle these cases?