From: Dave Hansen <dave.hansen@intel.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>,
Mel Gorman <mgorman@techsingularity.net>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Dan Williams <dan.j.williams@intel.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
David Hildenbrand <david@redhat.com>,
Jason Wang <jasowang@redhat.com>, Michal Hocko <mhocko@suse.com>,
Liang Li <liliangleo@didiglobal.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [RFC v2 PATCH 4/4] mm: pre zero out free pages to speed up page allocation for __GFP_ZERO
Date: Mon, 4 Jan 2021 11:51:38 -0800 [thread overview]
Message-ID: <a5ba7bdf-8510-d0a0-9c22-ec1b81019982@intel.com> (raw)
In-Reply-To: <20210104192753.GD22407@casper.infradead.org>
On 1/4/21 11:27 AM, Matthew Wilcox wrote:
> On Mon, Jan 04, 2021 at 11:19:13AM -0800, Dave Hansen wrote:
>> On 12/21/20 8:30 AM, Liang Li wrote:
>>> --- a/include/linux/page-flags.h
>>> +++ b/include/linux/page-flags.h
>>> @@ -137,6 +137,9 @@ enum pageflags {
>>> #endif
>>> #ifdef CONFIG_64BIT
>>> PG_arch_2,
>>> +#endif
>>> +#ifdef CONFIG_PREZERO_PAGE
>>> + PG_zero,
>>> #endif
>>> __NR_PAGEFLAGS,
>>
>> I don't think this is worth a generic page->flags bit.
>>
>> There's a ton of space in 'struct page' for pages that are in the
>> allocator. Can't we use some of that space?
>
> I was going to object to that too, but I think the entire approach is
> flawed and needs to be thrown out. It just nukes the caches in extremely
> subtle and hard to measure ways, lowering overall system performance.
Yeah, it certainly can't be the default, but it *is* useful for thing
where we know that there are no cache benefits to zeroing close to where
the memory is allocated.
The trick is opting into it somehow, either in a process or a VMA.
next prev parent reply other threads:[~2021-01-04 19:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-21 16:30 Liang Li
2021-01-04 19:19 ` Dave Hansen
2021-01-04 19:27 ` Matthew Wilcox
2021-01-04 19:44 ` Dan Williams
2021-01-04 19:51 ` Dave Hansen [this message]
2021-01-04 20:11 ` David Hildenbrand
2021-01-04 22:29 ` Dan Williams
2021-01-04 23:00 ` Dave Hansen
2021-01-05 9:20 ` Michal Hocko
2021-01-05 9:29 ` David Hildenbrand
2021-01-05 9:39 ` Liang Li
2021-01-05 9:56 ` Michal Hocko
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