linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Uladzislau Rezki <urezki@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Uladzislau Rezki <urezki@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH 2/2] mm/vmalloc: Use kvmalloc to allocate the table of pages
Date: Tue, 23 Mar 2021 21:39:24 +0100	[thread overview]
Message-ID: <20210323203924.GA52881@pc638.lan> (raw)
In-Reply-To: <20210323123913.GD1719932@casper.infradead.org>

> On Tue, Mar 23, 2021 at 01:04:36PM +0100, Uladzislau Rezki wrote:
> > On Mon, Mar 22, 2021 at 11:03:11PM +0000, Matthew Wilcox wrote:
> > > I suspect the vast majority of the time is spent calling alloc_pages_node()
> > > 1024 times.  Have you looked at Mel's patch to do ... well, exactly what
> > > vmalloc() wants?
> > > 
> > <snip>
> >          - __vmalloc_node_range
> >             - 45.25% __alloc_pages_nodemask
> >                - 37.59% get_page_from_freelist
> [...]
> >       - 44.61% 0xffffffffc047348d
> >          - __vunmap
> >             - 35.56% free_unref_page
> 
> Hmm!  I hadn't been thinking about the free side of things.
> Does this make a difference?
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 4f5f8c907897..61d5b769fea0 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2277,16 +2277,8 @@ static void __vunmap(const void *addr, int deallocate_pages)
>  	vm_remove_mappings(area, deallocate_pages);
>  
>  	if (deallocate_pages) {
> -		int i;
> -
> -		for (i = 0; i < area->nr_pages; i++) {
> -			struct page *page = area->pages[i];
> -
> -			BUG_ON(!page);
> -			__free_pages(page, 0);
> -		}
> +		release_pages(area->pages, area->nr_pages);
>  		atomic_long_sub(area->nr_pages, &nr_vmalloc_pages);
> -
>  		kvfree(area->pages);
>  	}
>
Same test. 4MB allocation on a single CPU:

default: loops: 1000000 avg: 93601889 usec
patch:   loops: 1000000 avg: 98217904 usec

<snip default>
            - __vunmap
               - 41.17% free_unref_page
                  - 28.42% free_pcppages_bulk
                     - 6.38% __mod_zone_page_state
                          4.79% check_preemption_disabled
                       2.63% __list_del_entry_valid
                       2.63% __list_add_valid
                  - 7.50% free_unref_page_commit
                       2.15% check_preemption_disabled
                       2.01% __list_add_valid
                    2.31% free_unref_page_prepare.part.86
                    0.70% free_pcp_prepare
<snip default>

<snip patch>
        - __vunmap
               - 45.36% release_pages
                  - 37.70% free_unref_page_list
                     - 24.70% free_pcppages_bulk
                        - 5.42% __mod_zone_page_state
                             4.23% check_preemption_disabled
                          2.31% __list_add_valid
                          2.07% __list_del_entry_valid
                     - 7.58% free_unref_page_commit
                          2.47% check_preemption_disabled
                          1.75% __list_add_valid
                       3.43% free_unref_page_prepare.part.86
                  - 2.39% mem_cgroup_uncharge_list
                       uncharge_page
<snip patch>

It is obvious that the default version is slightly better. It requires
less things to be done comparing with release_pages() variant.

> 
> release_pages does a bunch of checks that are unnecessary ... we could
> probably just do:
> 
> 		LIST_HEAD(pages_to_free);
> 
> 		for (i = 0; i < area->nr_pages; i++) {
> 			struct page *page = area->pages[i];
> 			if (put_page_testzero(page))
> 				list_add(&page->lru, &pages_to_free);
> 		}
> 		free_unref_page_list(&pages_to_free);
> 
> but let's see if the provided interface gets us the performance we want.
>  
I will test it tomorrow. From the first glance it looks like a more light version :)

--
Vlad Rezki


  parent reply	other threads:[~2021-03-23 20:39 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-22 19:38 [PATCH 1/2] mm/util: Add kvmalloc_node_caller Matthew Wilcox (Oracle)
2021-03-22 19:38 ` [PATCH 2/2] mm/vmalloc: Use kvmalloc to allocate the table of pages Matthew Wilcox (Oracle)
2021-03-22 22:36   ` Uladzislau Rezki
2021-03-22 23:03     ` Matthew Wilcox
2021-03-23 12:04       ` Uladzislau Rezki
2021-03-23 12:39         ` Matthew Wilcox
2021-03-23 13:39           ` Uladzislau Rezki
2021-03-23 14:07             ` Matthew Wilcox
2021-03-23 20:49               ` Uladzislau Rezki
2021-03-23 20:39           ` Uladzislau Rezki [this message]
2021-03-24 18:41             ` Uladzislau Rezki

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=20210323203924.GA52881@pc638.lan \
    --to=urezki@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=cl@linux.com \
    --cc=iamjoonsoo.kim@lge.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=npiggin@gmail.com \
    --cc=penberg@kernel.org \
    --cc=rientjes@google.com \
    --cc=vbabka@suse.cz \
    --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;
as well as URLs for NNTP newsgroup(s).