From: Matthew Wilcox <willy@infradead.org>
To: Hugh Dickins <hughd@google.com>
Cc: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org,
linux-hexagon@vger.kernel.org, loongarch@lists.linux.dev,
linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
linux-openrisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
linux-um@lists.infradead.org, xen-devel@lists.xenproject.org,
kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
Huacai Chen <chenhuacai@kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Dinh Nguyen <dinguyen@kernel.org>,
Jonas Bonn <jonas@southpole.se>,
David Hildenbrand <david@redhat.com>,
Claudio
Subject: Re: [PATCH mm-unstable v7 00/31] Split ptdesc from struct page
Date: Wed, 26 Jul 2023 15:34:17 +0100 [thread overview]
Message-ID: <ZMEu6VcTqPj69bQ7@casper.infradead.org> (raw)
In-Reply-To: <5296514f-cdd1-9526-2e83-a21e76e86e5@google.com>
On Mon, Jul 24, 2023 at 09:41:36PM -0700, Hugh Dickins wrote:
> On Mon, 24 Jul 2023, Vishal Moola (Oracle) wrote:
>
> > The MM subsystem is trying to shrink struct page. This patchset
> > introduces a memory descriptor for page table tracking - struct ptdesc.
> >
> > This patchset introduces ptdesc, splits ptdesc from struct page, and
> > converts many callers of page table constructor/destructors to use ptdescs.
> >
> > Ptdesc is a foundation to further standardize page tables, and eventually
> > allow for dynamic allocation of page tables independent of struct page.
> > However, the use of pages for page table tracking is quite deeply
> > ingrained and varied across archictectures, so there is still a lot of
> > work to be done before that can happen.
>
> Others may differ, but it remains the case that I see no point to this
> patchset, until the minimal descriptor that replaces struct page is
> working, and struct page then becomes just overhead. Until that time,
> let architectures continue to use struct page as they do - whyever not?
Because it's easier for architecture maintainers to understand what they
should and shouldn't be using. Look at the definition:
+struct ptdesc {
+ unsigned long __page_flags;
+
+ union {
+ struct rcu_head pt_rcu_head;
+ struct list_head pt_list;
+ struct {
+ unsigned long _pt_pad_1;
+ pgtable_t pmd_huge_pte;
+ };
+ };
+ unsigned long __page_mapping;
+
+ union {
+ struct mm_struct *pt_mm;
+ atomic_t pt_frag_refcount;
+ };
+
+ union {
+ unsigned long _pt_pad_2;
+#if ALLOC_SPLIT_PTLOCKS
+ spinlock_t *ptl;
+#else
+ spinlock_t ptl;
+#endif
+ };
+ unsigned int __page_type;
+ atomic_t _refcount;
+#ifdef CONFIG_MEMCG
+ unsigned long pt_memcg_data;
+#endif
+};
It's still a 31-line struct definition, I'll grant you. But it's far
easier to comprehend than the definition of struct page (~140 lines).
An architecture maintainer can look at it and see what might be available,
and what is already used. And hopefully we'll have less "Oh, I'll just
use page->private". It's really not fair to expect arch maintainers to
learn so much about the mm.
It's still messier than I would like, but I don't think we can do better
for now. I don't understand why you're so interested in delaying doing
this work.
prev parent reply other threads:[~2023-07-26 14:34 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-25 4:20 [PATCH mm-unstable v7 00/31] Split ptdesc from struct page Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 01/31] mm: Add PAGE_TYPE_OP folio functions Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 02/31] pgtable: Create struct ptdesc Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 03/31] mm: add utility functions for ptdesc Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 04/31] mm: Convert pmd_pgtable_page() callers to use pmd_ptdesc() Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 05/31] mm: Convert ptlock_alloc() to use ptdescs Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 06/31] mm: Convert ptlock_ptr() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 07/31] mm: Convert pmd_ptlock_init() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 08/31] mm: Convert ptlock_init() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 09/31] mm: Convert pmd_ptlock_free() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 10/31] mm: Convert ptlock_free() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 11/31] mm: Create ptdesc equivalents for pgtable_{pte,pmd}_page_{ctor,dtor} Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 12/31] powerpc: Convert various functions to use ptdescs Vishal Moola (Oracle)
2023-07-25 23:33 ` kernel test robot
2023-07-25 4:20 ` [PATCH mm-unstable v7 13/31] x86: " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 14/31] s390: Convert various pgalloc " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 15/31] mm: Remove page table members from struct page Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 16/31] pgalloc: Convert various functions to use ptdescs Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 17/31] arm: " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 18/31] arm64: " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 19/31] csky: Convert __pte_free_tlb() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 20/31] hexagon: " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 21/31] loongarch: Convert various functions " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 22/31] m68k: " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 23/31] mips: " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 24/31] nios2: Convert __pte_free_tlb() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 25/31] openrisc: " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 26/31] riscv: Convert alloc_{pmd, pte}_late() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 27/31] sh: Convert pte_free_tlb() " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 28/31] sparc64: Convert various functions " Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 29/31] sparc: Convert pgtable_pte_page_{ctor, dtor}() to ptdesc equivalents Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 30/31] um: Convert {pmd, pte}_free_tlb() to use ptdescs Vishal Moola (Oracle)
2023-07-25 4:20 ` [PATCH mm-unstable v7 31/31] mm: Remove pgtable_{pmd, pte}_page_{ctor, dtor}() wrappers Vishal Moola (Oracle)
2023-07-25 4:41 ` [PATCH mm-unstable v7 00/31] Split ptdesc from struct page Hugh Dickins
2023-07-26 14:34 ` Matthew Wilcox [this message]
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