From: Larry Bassel <larry.bassel@oracle.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Larry Bassel <larry.bassel@oracle.com>,
mike.kravetz@oracle.com, willy@infradead.org,
dan.j.williams@intel.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org
Subject: Re: [PATCH, RFC 0/2] Share PMDs for FS/DAX on x86
Date: Tue, 14 May 2019 09:09:06 -0700 [thread overview]
Message-ID: <20190514160906.GB27569@ubuette> (raw)
In-Reply-To: <20190514122820.26zddpb27uxgrwzp@box>
On 14 May 19 15:28, Kirill A. Shutemov wrote:
> On Thu, May 09, 2019 at 09:05:31AM -0700, Larry Bassel wrote:
> > This patchset implements sharing of page table entries pointing
> > to 2MiB pages (PMDs) for FS/DAX on x86.
>
> -EPARSE.
>
> How do you share entries? Entries do not take any space, page tables that
> cointain these entries do.
Yes, I'll correct this in v2.
>
> Have you checked if the patch makes memory consumption any better. I have
> doubts in it.
Yes I have -- the following is debugging output I have from my testing.
The (admittedly simple) test case is two copies of a program that mmaps
1GiB of a DAX/XFS file (with 2MiB page size), touches the first page
(physical 200400000 in this case) and then sleeps forever.
sharing disabled:
(process A)
[ 420.369975] pgd_index = fe
[ 420.369975] pgd = 00000000e1ebf83b
[ 420.369975] pgd_val = 8000000405ca8067
[ 420.369976] pud_index = 100
[ 420.369976] pud = 00000000bd7a7df0
[ 420.369976] pud_val = 4058f9067
[ 420.369977] pmd_index = 0
[ 420.369977] pmd = 00000000791e93d4
[ 420.369977] pmd_val = 84000002004008e7
[ 420.369978] pmd huge
[ 420.369978] page_addr = 200400000, page_offset = 0
[ 420.369979] vaddr = 7f4000000000, paddr = 200400000
(process B)
[ 420.370013] pgd_index = fe
[ 420.370014] pgd = 00000000a2bac60d
[ 420.370014] pgd_val = 8000000405a8f067
[ 420.370015] pud_index = 100
[ 420.370015] pud = 00000000dcc3ff1a
[ 420.370015] pud_val = 3fc713067
[ 420.370016] pmd_index = 0
[ 420.370016] pmd = 000000006b4679db
[ 420.370016] pmd_val = 84000002004008e7
[ 420.370017] pmd huge
[ 420.370017] page_addr = 200400000, page_offset = 0
[ 420.370018] vaddr = 7f4000000000, paddr = 200400000
sharing enabled:
(process A)
[ 696.992342] pgd_index = fe
[ 696.992342] pgd = 000000009612024b
[ 696.992343] pgd_val = 8000000404725067
[ 696.992343] pud_index = 100
[ 696.992343] pud = 00000000c98ab17c
[ 696.992344] pud_val = 4038e3067
[ 696.992344] pmd_index = 0
[ 696.992344] pmd = 000000002437681b
[ 696.992344] pmd_val = 84000002004008e7
[ 696.992345] pmd huge
[ 696.992345] page_addr = 200400000, page_offset = 0
[ 696.992345] vaddr = 7f4000000000, paddr = 200400000
(process B)
[ 696.992351] pgd_index = fe
[ 696.992351] pgd = 0000000012326848
[ 696.992352] pgd_val = 800000040a953067
[ 696.992352] pud_index = 100
[ 696.992352] pud = 00000000f989bcf6
[ 696.992352] pud_val = 4038e3067
[ 696.992353] pmd_index = 0
[ 696.992353] pmd = 000000002437681b
[ 696.992353] pmd_val = 84000002004008e7
[ 696.992353] pmd huge
[ 696.992354] page_addr = 200400000, page_offset = 0
[ 696.992354] vaddr = 7f4000000000, paddr = 200400000
Note that in the sharing enabled case, the pud_val and pmd are
the same for the two processes. In the disabled case we
have two separate pmds (and so more memory was allocated).
Also, (though not visible from the output above) the second
process did not take a page fault as the virtual->physical mapping
was already established thanks to the sharing.
Larry
prev parent reply other threads:[~2019-05-14 16:09 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-09 16:05 Larry Bassel
2019-05-09 16:05 ` [PATCH, RFC 1/2] Add config option to enable FS/DAX PMD sharing Larry Bassel
2019-05-10 16:32 ` Elliott, Robert (Servers)
2019-05-10 18:14 ` Dan Williams
2019-05-09 16:05 ` [PATCH, RFC 2/2] Implement sharing/unsharing of PMDs for FS/DAX Larry Bassel
2019-05-09 16:49 ` Matthew Wilcox
2019-05-10 16:16 ` Larry Bassel
2019-05-10 22:45 ` Mike Kravetz
2019-05-14 13:01 ` Kirill A. Shutemov
2019-05-24 16:07 ` Larry Bassel
2019-05-24 17:02 ` Dan Williams
2019-06-12 2:07 ` Kirill A. Shutemov
2019-05-14 12:28 ` [PATCH, RFC 0/2] Share PMDs for FS/DAX on x86 Kirill A. Shutemov
2019-05-14 16:09 ` Larry Bassel [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190514160906.GB27569@ubuette \
--to=larry.bassel@oracle.com \
--cc=dan.j.williams@intel.com \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-nvdimm@lists.01.org \
--cc=mike.kravetz@oracle.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox