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8e38607aa4
Patch series "mm: folio_zero_user: clear page ranges", v11.
This series adds clearing of contiguous page ranges for hugepages.
The series improves on the current discontiguous clearing approach in two
ways:
- clear pages in a contiguous fashion.
- use batched clearing via clear_pages() wherever exposed.
The first is useful because it allows us to make much better use of
hardware prefetchers.
The second, enables advertising the real extent to the processor. Where
specific instructions support it (ex. string instructions on x86; "mops"
on arm64 etc), a processor can optimize based on this because, instead of
seeing a sequence of 8-byte stores, or a sequence of 4KB pages, it sees a
larger unit being operated on.
For instance, AMD Zen uarchs (for extents larger than LLC-size) switch to
a mode where they start eliding cacheline allocation. This is helpful not
just because it results in higher bandwidth, but also because now the
cache is not evicting useful cachelines and replacing them with zeroes.
Demand faulting a 64GB region shows performance improvement:
$ perf bench mem mmap -p $pg-sz -f demand -s 64GB -l 5
baseline +series
(GBps +- %stdev) (GBps +- %stdev)
pg-sz=2MB 11.76 +- 1.10% 25.34 +- 1.18% [*] +115.47% preempt=*
pg-sz=1GB 24.85 +- 2.41% 39.22 +- 2.32% + 57.82% preempt=none|voluntary
pg-sz=1GB (similar) 52.73 +- 0.20% [#] +112.19% preempt=full|lazy
[*] This improvement is because switching to sequential clearing
allows the hardware prefetchers to do a much better job.
[#] For pg-sz=1GB a large part of the improvement is because of the
cacheline elision mentioned above. preempt=full|lazy improves upon
that because, not needing explicit invocations of cond_resched() to
ensure reasonable preemption latency, it can clear the full extent
as a single unit. In comparison the maximum extent used for
preempt=none|voluntary is PROCESS_PAGES_NON_PREEMPT_BATCH (32MB).
When provided the full extent the processor forgoes allocating
cachelines on this path almost entirely.
(The hope is that eventually, in the fullness of time, the lazy
preemption model will be able to do the same job that none or
voluntary models are used for, allowing us to do away with
cond_resched().)
Raghavendra also tested previous version of the series on AMD Genoa and
sees similar improvement [1] with preempt=lazy.
$ perf bench mem map -p $page-size -f populate -s 64GB -l 10
base patched change
pg-sz=2MB 12.731939 GB/sec 26.304263 GB/sec 106.6%
pg-sz=1GB 26.232423 GB/sec 61.174836 GB/sec 133.2%
This patch (of 8):
Let's drop all variants that effectively map to clear_page() and provide
it in a generic variant instead.
We'll use the macro clear_user_page to indicate whether an architecture
provides it's own variant.
Also, clear_user_page() is only called from the generic variant of
clear_user_highpage(), so define it only if the architecture does not
provide a clear_user_highpage(). And, for simplicity define it in
linux/highmem.h.
Note that for parisc, clear_page() and clear_user_page() map to
clear_page_asm(), so we can just get rid of the custom clear_user_page()
implementation. There is a clear_user_page_asm() function on parisc, that
seems to be unused. Not sure what's up with that.
Link: https://lkml.kernel.org/r/20260107072009.1615991-1-ankur.a.arora@oracle.com
Link: https://lkml.kernel.org/r/20260107072009.1615991-2-ankur.a.arora@oracle.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Co-developed-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzessutek Wilk <konrad.wilk@oracle.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@amd.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
87 lines
2 KiB
C
87 lines
2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ALPHA_PAGE_H
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#define _ALPHA_PAGE_H
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#include <linux/const.h>
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#include <asm/pal.h>
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#include <vdso/page.h>
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#ifndef __ASSEMBLER__
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#define STRICT_MM_TYPECHECKS
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extern void clear_page(void *page);
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#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
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vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
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extern void copy_page(void * _to, void * _from);
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#define copy_user_page(to, from, vaddr, pg) copy_page(to, from)
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#ifdef STRICT_MM_TYPECHECKS
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/*
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* These are used to make use of C type-checking..
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*/
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typedef struct { unsigned long pte; } pte_t;
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typedef struct { unsigned long pmd; } pmd_t;
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typedef struct { unsigned long pgd; } pgd_t;
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typedef struct { unsigned long pgprot; } pgprot_t;
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#define pte_val(x) ((x).pte)
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#define pmd_val(x) ((x).pmd)
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#define pgd_val(x) ((x).pgd)
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#define pgprot_val(x) ((x).pgprot)
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#define __pte(x) ((pte_t) { (x) } )
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#define __pmd(x) ((pmd_t) { (x) } )
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#define __pgd(x) ((pgd_t) { (x) } )
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#define __pgprot(x) ((pgprot_t) { (x) } )
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#else
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/*
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* .. while these make it easier on the compiler
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*/
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typedef unsigned long pte_t;
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typedef unsigned long pmd_t;
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typedef unsigned long pgd_t;
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typedef unsigned long pgprot_t;
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#define pte_val(x) (x)
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#define pmd_val(x) (x)
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#define pgd_val(x) (x)
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#define pgprot_val(x) (x)
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#define __pte(x) (x)
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#define __pgd(x) (x)
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#define __pgprot(x) (x)
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#endif /* STRICT_MM_TYPECHECKS */
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typedef struct page *pgtable_t;
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#ifdef USE_48_BIT_KSEG
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#define PAGE_OFFSET 0xffff800000000000UL
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#else
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#define PAGE_OFFSET 0xfffffc0000000000UL
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#endif
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#else
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#ifdef USE_48_BIT_KSEG
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#define PAGE_OFFSET 0xffff800000000000
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#else
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#define PAGE_OFFSET 0xfffffc0000000000
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#endif
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#endif /* !__ASSEMBLER__ */
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#define __pa(x) ((unsigned long) (x) - PAGE_OFFSET)
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#define __va(x) ((void *)((unsigned long) (x) + PAGE_OFFSET))
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#define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
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#define virt_addr_valid(kaddr) pfn_valid((__pa(kaddr) >> PAGE_SHIFT))
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#include <asm-generic/memory_model.h>
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#include <asm-generic/getorder.h>
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#endif /* _ALPHA_PAGE_H */
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