linux-kernel - Re: [PATCH v2 3/5] mm: add persistent huge zero folio

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Message-ID: <cgtgtq7ctkouzu6ki3nvzugw5txcgygtf6nducrqvbok7ajuhd@cqjtygxpsgnr>
Date: Mon, 11 Aug 2025 10:33:08 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: 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>, 
	David Hildenbrand <david@...hat.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, 
	willy@...radead.org, linux-mm@...ck.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 v2 3/5] mm: add persistent huge zero folio

> This is much nicer and now _super_ simple, I like it.

Thanks to you and David :)

> 
> A few nits below but generally:
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Thanks.
> 
> > ---
> >  include/linux/huge_mm.h | 16 ++++++++++++++++
> >  mm/Kconfig              | 16 ++++++++++++++++
> >  mm/huge_memory.c        | 40 ++++++++++++++++++++++++++++++----------
> >  3 files changed, 62 insertions(+), 10 deletions(-)
> >
> >  static inline int split_folio_to_list_to_order(struct folio *folio,
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > index e443fe8cd6cf..fbe86ef97fd0 100644
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -823,6 +823,22 @@ config ARCH_WANT_GENERAL_HUGETLB
> >  config ARCH_WANTS_THP_SWAP
> >  	def_bool n
> >
> > +config PERSISTENT_HUGE_ZERO_FOLIO
> > +	bool "Allocate a PMD sized folio for zeroing"
> > +	depends on TRANSPARENT_HUGEPAGE
> 
> I feel like we really need to sort out what is/isn't predicated on THP... it
> seems like THP is sort of short hand for 'any large folio stuff' but not
> always...
> 
> But this is a more general point :)

I already brought this topic once during THP cabal. I am thinking of
submitting a talk about this topic for LPC Memory Management MC.

> 
> > +	help
> > +	  Enable this option to reduce the runtime refcounting overhead
> > +	  of the huge zero folio and expand the places in the kernel
> > +	  that can use huge zero folios. This can potentially improve
> > +	  the performance while performing an I/O.
> 
> NIT: I think we can drop 'an', and probably refactor this sentence to something
> like 'For instance, block I/O benefits from access to large folios for zeroing
> memory'.
> 
> > +
> > +	  With this option enabled, the huge zero folio is allocated
> > +	  once and never freed. One full huge page worth of memory shall
> > +	  be used.
> 
> NIT: huge page worth -> huge page's worth
> 

Thanks for the comments. I will make those changes and send a new
version.

--
Pankaj