All of lore.kernel.org
 help / color / mirror / Atom feed
From: Pasha Tatashin <pasha.tatashin@soleen.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	linux-m68k@lists.linux-m68k.org,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Matthew Wilcox <willy@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	william.kucharski@oracle.com,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	schmitzmic@gmail.com, Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Roman Gushchin <guro@fb.com>,
	weixugc@google.com, Greg Thelen <gthelen@google.com>
Subject: Re: [RFC 1/8] mm: add overflow and underflow checks for page->_refcount
Date: Wed, 27 Oct 2021 14:22:08 -0400	[thread overview]
Message-ID: <CA+CK2bA1mj3B8Y47r8KG7oYCNn63WsjUZeyAdOkThjixxqxGPQ@mail.gmail.com> (raw)
In-Reply-To: <CAMZfGtVS2ZRAsd9HLODoLa1vVp0XCcBOTXjsmpoWwDcdGaADvQ@mail.gmail.com>

> I found some atomic_add/dec are replaced with atomic_add/dec_return,

I am going to replace -return variants with -fetch variants, potentially -fetch

> those helpers with return value imply a full memory barrier around it, but
> others without return value do not. Do you have any numbers to show
> the impact? Maybe atomic_add/dec_return_relaxed can help this.

The generic variant uses  arch_cmpxchg() for all atomic variants
without any extra barriers. Therefore, on platforms that use generic
implementations there won't be performance differences except for an
extra branch that checks results when VM_BUG_ON is enabled.

On x86 the difference between the two is the following

atomic_add:
   lock add %eax,(%rsi)

atomic_fetch_add:
   lock xadd %eax,(%rsi)

atomic_fetch_add_relaxed:
   lock xadd %eax,(%rsi)

No differences between relaxed and non relaxed variants. However, we
used lock xadd instead of lock add. I am not sure if the performance
difference is going to be different.

Pasha

  reply	other threads:[~2021-10-27 18:22 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-26 17:38 [RFC 0/8] Hardening page _refcount Pasha Tatashin
2021-10-26 17:38 ` [RFC 1/8] mm: add overflow and underflow checks for page->_refcount Pasha Tatashin
2021-10-26 19:48   ` Matthew Wilcox
2021-10-26 21:34     ` Pasha Tatashin
2021-10-27  1:21       ` Pasha Tatashin
2021-10-27  3:04         ` Matthew Wilcox
2021-10-27 18:22           ` Pasha Tatashin
2021-10-27  7:46   ` Muchun Song
2021-10-27 18:22     ` Pasha Tatashin [this message]
2021-10-28  4:08       ` Muchun Song
2021-10-26 17:38 ` [RFC 2/8] mm/hugetlb: remove useless set_page_count() Pasha Tatashin
2021-10-26 18:44   ` Mike Kravetz
2021-10-26 18:50     ` Pasha Tatashin
2021-10-26 21:19       ` Mike Kravetz
2021-10-26 17:38 ` [RFC 3/8] mm: Avoid using set_page_count() in set_page_recounted() Pasha Tatashin
2021-10-26 17:53   ` John Hubbard
2021-10-26 18:01     ` John Hubbard
2021-10-26 18:14       ` Pasha Tatashin
2021-10-26 18:21     ` Pasha Tatashin
2021-10-27  5:12       ` John Hubbard
2021-10-27 18:27         ` Pasha Tatashin
2021-10-28  1:20           ` John Hubbard
2021-10-28  1:35             ` John Hubbard
2021-11-01 14:30               ` Pasha Tatashin
2021-11-01 19:35                 ` John Hubbard
2021-11-01 14:22             ` Pasha Tatashin
2021-11-01 19:31               ` John Hubbard
2021-11-01 19:42               ` John Hubbard
2021-10-26 17:38 ` [RFC 4/8] mm: remove set_page_count() from page_frag_alloc_align Pasha Tatashin
2021-10-26 17:38 ` [RFC 5/8] mm: avoid using set_page_count() when pages are freed into allocator Pasha Tatashin
2021-10-26 17:38 ` [RFC 6/8] mm: rename init_page_count() -> page_ref_init() Pasha Tatashin
2021-10-27  6:46   ` Geert Uytterhoeven
2021-10-26 17:38 ` [RFC 7/8] mm: remove set_page_count() Pasha Tatashin
2021-10-26 17:38 ` [RFC 8/8] mm: simplify page_ref_* functions Pasha Tatashin
2021-10-26 18:23 ` [RFC 0/8] Hardening page _refcount Matthew Wilcox
2021-10-26 18:30   ` Pasha Tatashin
2021-10-26 20:13     ` Matthew Wilcox
2021-10-26 21:24       ` Pasha Tatashin

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=CA+CK2bA1mj3B8Y47r8KG7oYCNn63WsjUZeyAdOkThjixxqxGPQ@mail.gmail.com \
    --to=pasha.tatashin@soleen.com \
    --cc=akpm@linux-foundation.org \
    --cc=anshuman.khandual@arm.com \
    --cc=geert@linux-m68k.org \
    --cc=gthelen@google.com \
    --cc=guro@fb.com \
    --cc=hannes@cmpxchg.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-m68k@lists.linux-m68k.org \
    --cc=linux-mm@kvack.org \
    --cc=mike.kravetz@oracle.com \
    --cc=mingo@redhat.com \
    --cc=rostedt@goodmis.org \
    --cc=schmitzmic@gmail.com \
    --cc=songmuchun@bytedance.com \
    --cc=vbabka@suse.cz \
    --cc=weixugc@google.com \
    --cc=william.kucharski@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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.