From: Yu Zhao <yuzhao@google.com>
To: Yang Shi <shy828301@gmail.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Alexander Duyck" <alexander.h.duyck@linux.intel.com>,
"Huang Ying" <ying.huang@intel.com>,
"David Hildenbrand" <david@redhat.com>,
"Michal Hocko" <mhocko@suse.com>,
"Yang Shi" <yang.shi@linux.alibaba.com>, "Qian Cai" <cai@lca.pw>,
"Mel Gorman" <mgorman@suse.de>,
"Nicholas Piggin" <npiggin@gmail.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Hugh Dickins" <hughd@google.com>,
"Linux MM" <linux-mm@kvack.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Joonsoo Kim" <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH v2 3/3] mm: remove superfluous __ClearPageWaiters()
Date: Wed, 19 Aug 2020 17:39:16 -0600 [thread overview]
Message-ID: <20200819233916.GA2021304@google.com> (raw)
In-Reply-To: <CAHbLzkr7oPFtUog1zJWs54dsS8dhwkWp6ET_Zk71nXmRMtGvDQ@mail.gmail.com>
On Wed, Aug 19, 2020 at 04:06:32PM -0700, Yang Shi wrote:
> On Tue, Aug 18, 2020 at 11:47 AM Yu Zhao <yuzhao@google.com> wrote:
> >
> > Presumably __ClearPageWaiters() was added to follow the previously
> > removed __ClearPageActive() pattern.
> >
> > Only flags that are in PAGE_FLAGS_CHECK_AT_FREE needs to be properly
> > cleared because otherwise we think there may be some kind of leak.
> > PG_waiters is not one of those flags and leaving the clearing to
> > PAGE_FLAGS_CHECK_AT_PREP is more appropriate.
>
> Actually TBH I'm not very keen to this change, it seems the clearing
> is just moved around and the allocation side pays for that instead of
> free side.
I'll assume you are referring to the overhead from clearing
PG_waiters. First of all, there is no overhead -- we should have a
serious talk with the hardware team who makes word-size bitwise AND
more than one instruction. And the clearing is done in
free_pages_prepare(), which has nothing to do with allocations.
next prev parent reply other threads:[~2020-08-19 23:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-18 18:47 [PATCH v2 1/3] mm: remove activate_page() from unuse_pte() Yu Zhao
2020-08-18 18:47 ` [PATCH v2 2/3] mm: remove superfluous __ClearPageActive() Yu Zhao
2020-08-19 23:04 ` Yang Shi
2020-08-18 18:47 ` [PATCH v2 3/3] mm: remove superfluous __ClearPageWaiters() Yu Zhao
2020-08-19 23:06 ` Yang Shi
2020-08-19 23:39 ` Yu Zhao [this message]
2020-08-20 0:16 ` Yang Shi
2020-08-20 6:18 ` Michal Hocko
2020-08-20 8:12 ` Yu Zhao
2020-08-19 22:16 ` [PATCH v2 1/3] mm: remove activate_page() from unuse_pte() Yang Shi
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