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author | Kirill A. Shutemov <kirill.shutemov@linux.intel.com> | 2017-09-09 00:56:03 +0300 |
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committer | Ingo Molnar <mingo@kernel.org> | 2017-09-13 11:26:52 +0200 |
commit | 5b65c4677a57a1d4414212f9995aa0e46a21ff80 (patch) | |
tree | 0b47579035adebb1af14f009abf355e447ced9b0 | |
parent | 9e52fc2b50de3a1c08b44f94c610fbe998c0031a (diff) | |
download | linux-5b65c4677a57a1d4414212f9995aa0e46a21ff80.tar.gz linux-5b65c4677a57a1d4414212f9995aa0e46a21ff80.tar.bz2 linux-5b65c4677a57a1d4414212f9995aa0e46a21ff80.zip |
mm, x86/mm: Fix performance regression in get_user_pages_fast()
The 0-day test bot found a performance regression that was tracked down to
switching x86 to the generic get_user_pages_fast() implementation:
http://lkml.kernel.org/r/20170710024020.GA26389@yexl-desktop
The regression was caused by the fact that we now use local_irq_save() +
local_irq_restore() in get_user_pages_fast() to disable interrupts.
In x86 implementation local_irq_disable() + local_irq_enable() was used.
The fix is to make get_user_pages_fast() use local_irq_disable(),
leaving local_irq_save() for __get_user_pages_fast() that can be called
with interrupts disabled.
Numbers for pinning a gigabyte of memory, one page a time, 20 repeats:
Before: Average: 14.91 ms, stddev: 0.45 ms
After: Average: 10.76 ms, stddev: 0.18 ms
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thorsten Leemhuis <regressions@leemhuis.info>
Cc: linux-mm@kvack.org
Fixes: e585513b76f7 ("x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation")
Link: http://lkml.kernel.org/r/20170908215603.9189-3-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r-- | mm/gup.c | 97 |
1 files changed, 58 insertions, 39 deletions
@@ -1618,6 +1618,47 @@ static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end, return 1; } +static void gup_pgd_range(unsigned long addr, unsigned long end, + int write, struct page **pages, int *nr) +{ + unsigned long next; + pgd_t *pgdp; + + pgdp = pgd_offset(current->mm, addr); + do { + pgd_t pgd = READ_ONCE(*pgdp); + + next = pgd_addr_end(addr, end); + if (pgd_none(pgd)) + return; + if (unlikely(pgd_huge(pgd))) { + if (!gup_huge_pgd(pgd, pgdp, addr, next, write, + pages, nr)) + return; + } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) { + if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, + PGDIR_SHIFT, next, write, pages, nr)) + return; + } else if (!gup_p4d_range(pgd, addr, next, write, pages, nr)) + return; + } while (pgdp++, addr = next, addr != end); +} + +#ifndef gup_fast_permitted +/* + * Check if it's allowed to use __get_user_pages_fast() for the range, or + * we need to fall back to the slow version: + */ +bool gup_fast_permitted(unsigned long start, int nr_pages, int write) +{ + unsigned long len, end; + + len = (unsigned long) nr_pages << PAGE_SHIFT; + end = start + len; + return end >= start; +} +#endif + /* * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to * the regular GUP. It will only return non-negative values. @@ -1625,10 +1666,8 @@ static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end, int __get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages) { - struct mm_struct *mm = current->mm; unsigned long addr, len, end; - unsigned long next, flags; - pgd_t *pgdp; + unsigned long flags; int nr = 0; start &= PAGE_MASK; @@ -1652,45 +1691,15 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write, * block IPIs that come from THPs splitting. */ - local_irq_save(flags); - pgdp = pgd_offset(mm, addr); - do { - pgd_t pgd = READ_ONCE(*pgdp); - - next = pgd_addr_end(addr, end); - if (pgd_none(pgd)) - break; - if (unlikely(pgd_huge(pgd))) { - if (!gup_huge_pgd(pgd, pgdp, addr, next, write, - pages, &nr)) - break; - } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) { - if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, - PGDIR_SHIFT, next, write, pages, &nr)) - break; - } else if (!gup_p4d_range(pgd, addr, next, write, pages, &nr)) - break; - } while (pgdp++, addr = next, addr != end); - local_irq_restore(flags); + if (gup_fast_permitted(start, nr_pages, write)) { + local_irq_save(flags); + gup_pgd_range(addr, end, write, pages, &nr); + local_irq_restore(flags); + } return nr; } -#ifndef gup_fast_permitted -/* - * Check if it's allowed to use __get_user_pages_fast() for the range, or - * we need to fall back to the slow version: - */ -bool gup_fast_permitted(unsigned long start, int nr_pages, int write) -{ - unsigned long len, end; - - len = (unsigned long) nr_pages << PAGE_SHIFT; - end = start + len; - return end >= start; -} -#endif - /** * get_user_pages_fast() - pin user pages in memory * @start: starting user address @@ -1710,12 +1719,22 @@ bool gup_fast_permitted(unsigned long start, int nr_pages, int write) int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages) { + unsigned long addr, len, end; int nr = 0, ret = 0; start &= PAGE_MASK; + addr = start; + len = (unsigned long) nr_pages << PAGE_SHIFT; + end = start + len; + + if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, + (void __user *)start, len))) + return 0; if (gup_fast_permitted(start, nr_pages, write)) { - nr = __get_user_pages_fast(start, nr_pages, write, pages); + local_irq_disable(); + gup_pgd_range(addr, end, write, pages, &nr); + local_irq_enable(); ret = nr; } |