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Message-ID: <20210104192753.GD22407@casper.infradead.org>
Date: Mon, 4 Jan 2021 19:27:53 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
Mel Gorman <mgorman@...hsingularity.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrea Arcangeli <aarcange@...hat.com>,
Dan Williams <dan.j.williams@...el.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
David Hildenbrand <david@...hat.com>,
Jason Wang <jasowang@...hat.com>,
Michal Hocko <mhocko@...e.com>,
Liang Li <liliangleo@...iglobal.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org
Subject: Re: [RFC v2 PATCH 4/4] mm: pre zero out free pages to speed up page
allocation for __GFP_ZERO
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.
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