From: William Kucharski <william.kucharski@oracle.com>
To: Christopher Lameter <cl@linux.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC] mm, THP: Map read-only text segments using large THP pages
Date: Tue, 15 May 2018 00:59:16 -0600 [thread overview]
Message-ID: <D4359A94-6E95-4D89-B9F3-7A6CDB50C0A1@oracle.com> (raw)
In-Reply-To: <010001635f3c42d3-ed92871f-4fba-47dc-9750-69a40dd07ab6-000000@email.amazonses.com>
> On May 14, 2018, at 9:19 AM, Christopher Lameter <cl@linux.com> wrote:
>
> Cool. This could be controlled by the faultaround logic right? If we get
> fault_around_bytes up to huge page size then it is reasonable to use a
> huge page directly.
It isn't presently but certainly could be; for the prototype it tries to
map a large page when needed and, should that fail, it will fall through
to the normal fault around code.
I would think we would want a separate parameter, as I can see the usefulness
of more fine-grained control. Many users may want to try mapping a large page
if possible, but would prefer a smaller number of bytes to be read in fault
around should we need to fall back to using PAGESIZE pages.
> fault_around_bytes can be set via sysfs so there is a natural way to
> control this feature there I think.
I agree; perhaps I could use "fault_around_thp_bytes" or something similar.
>> Since this approach will map a PMD size block of the memory map at a time, we
>> should see a slight uptick in time spent in disk I/O but a substantial drop in
>> page faults as well as a reduction in iTLB misses as address ranges will be
>> mapped with the larger page. Analysis of a test program that consists of a very
>> large text area (483,138,032 bytes in size) that thrashes D$ and I$ shows this
>> does occur and there is a slight reduction in program execution time.
>
> I think we would also want such a feature for regular writable pages as
> soon as possible.
That is my ultimate long-term goal for this project - full r/w support of large
THP pages; prototyping with read-only text pages seemed like the best first step
to get a sense of the possible benefits.
-- Bill
next prev parent reply other threads:[~2018-05-15 6:59 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-14 13:12 [RFC] mm, THP: Map read-only text segments using large THP pages William Kucharski
2018-05-14 15:19 ` Christopher Lameter
2018-05-15 6:59 ` William Kucharski [this message]
2018-05-17 7:57 ` Michal Hocko
2018-05-17 14:34 ` William Kucharski
2018-05-17 15:23 ` Matthew Wilcox
2018-05-17 15:40 ` Larry Bassel
2018-05-17 17:31 ` William Kucharski
2018-05-20 6:26 ` Song Liu
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