linux-kernel - Re: [PATCH v3 0/5] add persistent huge zero folio support

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Message-ID: <osippshkfu7ip5tg42zc5nyxegrplm2kekskhitrapzjdyps3h@hodqaqh5r26o>
Date: Mon, 11 Aug 2025 11:36:29 +0100
From: Kiryl Shutsemau <kirill@...temov.name>
To: David Hildenbrand <david@...hat.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>, Suren Baghdasaryan <surenb@...gle.com>, 
	Ryan Roberts <ryan.roberts@....com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>, Mike Rapoport <rppt@...nel.org>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Michal Hocko <mhocko@...e.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Nico Pache <npache@...hat.com>, Dev Jain <dev.jain@....com>, 
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, willy@...radead.org, Ritesh Harjani <ritesh.list@...il.com>, 
	linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	"Darrick J . Wong" <djwong@...nel.org>, mcgrof@...nel.org, gost.dev@...sung.com, hch@....de, 
	Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH v3 0/5] add persistent huge zero folio support

On Mon, Aug 11, 2025 at 12:21:23PM +0200, David Hildenbrand wrote:
> On 11.08.25 12:17, Kiryl Shutsemau wrote:
> > On Mon, Aug 11, 2025 at 11:09:24AM +0100, Lorenzo Stoakes wrote:
> > > On Mon, Aug 11, 2025 at 11:07:48AM +0100, Kiryl Shutsemau wrote:
> > > > 
> > > > Well, my worry is that 2M can be a high tax for smaller machines.
> > > > Compile-time might be cleaner, but it has downsides.
> > > > 
> > > > It is also not clear if these users actually need physical HZP or virtual
> > > > is enough. Virtual is cheap.
> > > 
> > > The kernel config flag (default =N) literally says don't use unless you
> > > have plenty of memory :)
> > > 
> > > So this isn't an issue.
> > 
> > Distros use one-config-fits-all approach. Default N doesn't help
> > anything.
> 
> You'd probably want a way to say "use the persistent huge zero folio if you
> machine has more than X Gigs". That's all reasonable stuff that can be had
> on top of this series.

We have 'totalram_pages() < (512 << (20 - PAGE_SHIFT))' check in
hugepage_init(). It can [be abstracted out and] re-used.

-- 
Kiryl Shutsemau / Kirill A. Shutemov