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From: Peter Xu <peterx@redhat.com>
To: LEROY Christophe <christophe.leroy2@cs-soprasteria.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	David Hildenbrand <david@redhat.com>,
	Oscar Salvador <osalvador@suse.de>,
	"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Michal Hocko <mhocko@kernel.org>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	"x86@kernel.org" <x86@kernel.org>,
	Alistair Popple <apopple@nvidia.com>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Ryan Roberts <ryan.roberts@arm.com>,
	Hugh Dickins <hughd@google.com>,
	Axel Rasmussen <axelrasmussen@google.com>
Subject: Re: [PATCH RFC 2/6] mm: PGTABLE_HAS_P[MU]D_LEAVES config options
Date: Mon, 26 Aug 2024 10:34:39 -0400	[thread overview]
Message-ID: <ZsySf2F9djR5YVOr@x1n> (raw)
In-Reply-To: <d3e4256f-253a-4a61-a83b-93f50ebabed8@cs-soprasteria.com>

On Fri, Aug 23, 2024 at 06:19:52AM +0000, LEROY Christophe wrote:
> Why is an option needed for that ? If pmd_leaf() returns always false, 
> it means the arch doesn't support pmd mappings and if properly used all 
> related code should fold away without a config option, shouldn't it ?

It's not always easy to leverage an "if" clause there, IIUC.  Take the case
of when a driver wants to inject a pmd pfnmap, we may want something like:

  if (pmd_leaf_supported())
      inject_pmd_leaf(&pmd);

We don't have a pmd entry to reference at the point of pmd_leaf_supported()
when making the decision.

Thanks,

-- 
Peter Xu


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linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID (diff)
From: Peter Xu <peterx@redhat.com>
To: LEROY Christophe <christophe.leroy2@cs-soprasteria.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	David Hildenbrand <david@redhat.com>,
	Oscar Salvador <osalvador@suse.de>,
	"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Michal Hocko <mhocko@kernel.org>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	"x86@kernel.org" <x86@kernel.org>,
	Alistair Popple <apopple@nvidia.com>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Ryan Roberts <ryan.roberts@arm.com>,
	Hugh Dickins <hughd@google.com>,
	Axel Rasmussen <axelrasmussen@google.com>
Subject: Re: [PATCH RFC 2/6] mm: PGTABLE_HAS_P[MU]D_LEAVES config options
Date: Mon, 26 Aug 2024 10:34:39 -0400	[thread overview]
Message-ID: <ZsySf2F9djR5YVOr@x1n> (raw)
In-Reply-To: <d3e4256f-253a-4a61-a83b-93f50ebabed8@cs-soprasteria.com>

On Fri, Aug 23, 2024 at 06:19:52AM +0000, LEROY Christophe wrote:
> Why is an option needed for that ? If pmd_leaf() returns always false, 
> it means the arch doesn't support pmd mappings and if properly used all 
> related code should fold away without a config option, shouldn't it ?

It's not always easy to leverage an "if" clause there, IIUC.  Take the case
of when a driver wants to inject a pmd pfnmap, we may want something like:

  if (pmd_leaf_supported())
      inject_pmd_leaf(&pmd);

We don't have a pmd entry to reference at the point of pmd_leaf_supported()
when making the decision.

Thanks,

-- 
Peter Xu


  reply	other threads:[~2024-08-26 14:35 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-07-17 22:02 [PATCH RFC 0/6] mm: THP-agnostic refactor on huge mappings Peter Xu
2024-07-17 22:02 ` Peter Xu
2024-07-17 22:02 ` Peter Xu
2024-07-17 22:02 ` [PATCH RFC 1/6] mm/treewide: Remove pgd_devmap() Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02 ` [PATCH RFC 2/6] mm: PGTABLE_HAS_P[MU]D_LEAVES config options Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-08-22 17:22   ` LEROY Christophe
2024-08-22 17:22     ` LEROY Christophe
2024-08-22 19:16     ` Peter Xu
2024-08-22 19:16       ` Peter Xu
2024-08-23  6:19       ` LEROY Christophe
2024-08-23  6:19         ` LEROY Christophe
2024-08-26 14:34         ` Peter Xu [this message]
2024-08-26 14:34           ` Peter Xu
2024-07-17 22:02 ` [PATCH RFC 3/6] mm/treewide: Make pgtable-generic.c THP agnostic Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02 ` [PATCH RFC 4/6] mm: Move huge mapping declarations from internal.h to huge_mm.h Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02 ` [PATCH RFC 5/6] mm/huge_mapping: Create huge_mapping_pxx.c Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02 ` [PATCH RFC 6/6] mm: Convert "*_trans_huge() || *_devmap()" to use *_leaf() Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-17 22:02   ` Peter Xu
2024-07-22 13:29 ` [PATCH RFC 0/6] mm: THP-agnostic refactor on huge mappings David Hildenbrand
2024-07-22 13:29   ` David Hildenbrand
2024-07-22 13:29   ` David Hildenbrand
2024-07-22 15:31   ` Peter Xu
2024-07-22 15:31     ` Peter Xu
2024-07-22 15:31     ` Peter Xu
2024-07-23  8:18     ` David Hildenbrand
2024-07-23  8:18       ` David Hildenbrand
2024-07-23  8:18       ` David Hildenbrand
2024-07-23 21:04       ` Peter Xu
2024-07-23 21:04         ` Peter Xu
2024-07-23 21:04         ` Peter Xu
2024-07-23 21:22         ` David Hildenbrand
2024-07-23 21:22           ` David Hildenbrand
2024-07-23 21:22           ` David Hildenbrand
2024-08-22 17:08         ` LEROY Christophe
2024-08-22 17:08           ` LEROY Christophe

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