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Message-ID: <507D2E83.4010702@gmail.com>
Date: Tue, 16 Oct 2012 17:53:07 +0800
From: Ni zhan Chen <nizhan.chen@...il.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
Andi Kleen <ak@...ux.intel.com>,
"H. Peter Anvin" <hpa@...ux.intel.com>,
linux-kernel@...r.kernel.org,
"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v4 00/10, REBASED] Introduce huge zero page
On 10/15/2012 02:00 PM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>
> Hi,
>
> Andrew, here's huge zero page patchset rebased to v3.7-rc1.
>
> Andrea, I've dropped your Reviewed-by due not-so-trivial conflicts in during
> rebase. Could you look through it again. Patches 2, 3, 4, 7, 10 had conflicts.
> Mostly due new MMU notifiers interface.
>
> =================
>
> During testing I noticed big (up to 2.5 times) memory consumption overhead
> on some workloads (e.g. ft.A from NPB) if THP is enabled.
>
> The main reason for that big difference is lacking zero page in THP case.
> We have to allocate a real page on read page fault.
>
> A program to demonstrate the issue:
> #include <assert.h>
> #include <stdlib.h>
> #include <unistd.h>
>
> #define MB 1024*1024
>
> int main(int argc, char **argv)
> {
> char *p;
> int i;
>
> posix_memalign((void **)&p, 2 * MB, 200 * MB);
> for (i = 0; i < 200 * MB; i+= 4096)
> assert(p[i] == 0);
> pause();
> return 0;
> }
>
> With thp-never RSS is about 400k, but with thp-always it's 200M.
> After the patcheset thp-always RSS is 400k too.
>
> Design overview.
>
> Huge zero page (hzp) is a non-movable huge page (2M on x86-64) filled with
> zeros. The way how we allocate it changes in the patchset:
>
> - [01/10] simplest way: hzp allocated on boot time in hugepage_init();
> - [09/10] lazy allocation on first use;
> - [10/10] lockless refcounting + shrinker-reclaimable hzp;
>
> We setup it in do_huge_pmd_anonymous_page() if area around fault address
> is suitable for THP and we've got read page fault.
> If we fail to setup hzp (ENOMEM) we fallback to handle_pte_fault() as we
> normally do in THP.
>
> On wp fault to hzp we allocate real memory for the huge page and clear it.
> If ENOMEM, graceful fallback: we create a new pmd table and set pte around
> fault address to newly allocated normal (4k) page. All other ptes in the
> pmd set to normal zero page.
>
> We cannot split hzp (and it's bug if we try), but we can split the pmd
> which points to it. On splitting the pmd we create a table with all ptes
> set to normal zero page.
>
> Patchset organized in bisect-friendly way:
> Patches 01-07: prepare all code paths for hzp
> Patch 08: all code paths are covered: safe to setup hzp
> Patch 09: lazy allocation
> Patch 10: lockless refcounting for hzp
>
> v4:
> - Rebase to v3.7-rc1;
> - Update commit message;
> v3:
> - fix potential deadlock in refcounting code on preemptive kernel.
> - do not mark huge zero page as movable.
> - fix typo in comment.
> - Reviewed-by tag from Andrea Arcangeli.
> v2:
> - Avoid find_vma() if we've already had vma on stack.
> Suggested by Andrea Arcangeli.
> - Implement refcounting for huge zero page.
>
> --------------------------------------------------------------------------
>
> By hpa request I've tried alternative approach for hzp implementation (see
> Virtual huge zero page patchset): pmd table with all entries set to zero
> page. This way should be more cache friendly, but it increases TLB
> pressure.
Thanks for your excellent works. But could you explain me why current
implementation not cache friendly and hpa's request cache friendly?
Thanks in advance.
>
> The problem with virtual huge zero page: it requires per-arch enabling.
> We need a way to mark that pmd table has all ptes set to zero page.
>
> Some numbers to compare two implementations (on 4s Westmere-EX):
>
> Mirobenchmark1
> ==============
>
> test:
> posix_memalign((void **)&p, 2 * MB, 8 * GB);
> for (i = 0; i < 100; i++) {
> assert(memcmp(p, p + 4*GB, 4*GB) == 0);
> asm volatile ("": : :"memory");
> }
>
> hzp:
> Performance counter stats for './test_memcmp' (5 runs):
>
> 32356.272845 task-clock # 0.998 CPUs utilized ( +- 0.13% )
> 40 context-switches # 0.001 K/sec ( +- 0.94% )
> 0 CPU-migrations # 0.000 K/sec
> 4,218 page-faults # 0.130 K/sec ( +- 0.00% )
> 76,712,481,765 cycles # 2.371 GHz ( +- 0.13% ) [83.31%]
> 36,279,577,636 stalled-cycles-frontend # 47.29% frontend cycles idle ( +- 0.28% ) [83.35%]
> 1,684,049,110 stalled-cycles-backend # 2.20% backend cycles idle ( +- 2.96% ) [66.67%]
> 134,355,715,816 instructions # 1.75 insns per cycle
> # 0.27 stalled cycles per insn ( +- 0.10% ) [83.35%]
> 13,526,169,702 branches # 418.039 M/sec ( +- 0.10% ) [83.31%]
> 1,058,230 branch-misses # 0.01% of all branches ( +- 0.91% ) [83.36%]
>
> 32.413866442 seconds time elapsed ( +- 0.13% )
>
> vhzp:
> Performance counter stats for './test_memcmp' (5 runs):
>
> 30327.183829 task-clock # 0.998 CPUs utilized ( +- 0.13% )
> 38 context-switches # 0.001 K/sec ( +- 1.53% )
> 0 CPU-migrations # 0.000 K/sec
> 4,218 page-faults # 0.139 K/sec ( +- 0.01% )
> 71,964,773,660 cycles # 2.373 GHz ( +- 0.13% ) [83.35%]
> 31,191,284,231 stalled-cycles-frontend # 43.34% frontend cycles idle ( +- 0.40% ) [83.32%]
> 773,484,474 stalled-cycles-backend # 1.07% backend cycles idle ( +- 6.61% ) [66.67%]
> 134,982,215,437 instructions # 1.88 insns per cycle
> # 0.23 stalled cycles per insn ( +- 0.11% ) [83.32%]
> 13,509,150,683 branches # 445.447 M/sec ( +- 0.11% ) [83.34%]
> 1,017,667 branch-misses # 0.01% of all branches ( +- 1.07% ) [83.32%]
>
> 30.381324695 seconds time elapsed ( +- 0.13% )
Could you tell me which data I should care in this performance counter.
And what's the benefit of your current implementation compare to hpa's
request?
>
> Mirobenchmark2
> ==============
>
> test:
> posix_memalign((void **)&p, 2 * MB, 8 * GB);
> for (i = 0; i < 1000; i++) {
> char *_p = p;
> while (_p < p+4*GB) {
> assert(*_p == *(_p+4*GB));
> _p += 4096;
> asm volatile ("": : :"memory");
> }
> }
>
> hzp:
> Performance counter stats for 'taskset -c 0 ./test_memcmp2' (5 runs):
>
> 3505.727639 task-clock # 0.998 CPUs utilized ( +- 0.26% )
> 9 context-switches # 0.003 K/sec ( +- 4.97% )
> 4,384 page-faults # 0.001 M/sec ( +- 0.00% )
> 8,318,482,466 cycles # 2.373 GHz ( +- 0.26% ) [33.31%]
> 5,134,318,786 stalled-cycles-frontend # 61.72% frontend cycles idle ( +- 0.42% ) [33.32%]
> 2,193,266,208 stalled-cycles-backend # 26.37% backend cycles idle ( +- 5.51% ) [33.33%]
> 9,494,670,537 instructions # 1.14 insns per cycle
> # 0.54 stalled cycles per insn ( +- 0.13% ) [41.68%]
> 2,108,522,738 branches # 601.451 M/sec ( +- 0.09% ) [41.68%]
> 158,746 branch-misses # 0.01% of all branches ( +- 1.60% ) [41.71%]
> 3,168,102,115 L1-dcache-loads
> # 903.693 M/sec ( +- 0.11% ) [41.70%]
> 1,048,710,998 L1-dcache-misses
> # 33.10% of all L1-dcache hits ( +- 0.11% ) [41.72%]
> 1,047,699,685 LLC-load
> # 298.854 M/sec ( +- 0.03% ) [33.38%]
> 2,287 LLC-misses
> # 0.00% of all LL-cache hits ( +- 8.27% ) [33.37%]
> 3,166,187,367 dTLB-loads
> # 903.147 M/sec ( +- 0.02% ) [33.35%]
> 4,266,538 dTLB-misses
> # 0.13% of all dTLB cache hits ( +- 0.03% ) [33.33%]
>
> 3.513339813 seconds time elapsed ( +- 0.26% )
>
> vhzp:
> Performance counter stats for 'taskset -c 0 ./test_memcmp2' (5 runs):
>
> 27313.891128 task-clock # 0.998 CPUs utilized ( +- 0.24% )
> 62 context-switches # 0.002 K/sec ( +- 0.61% )
> 4,384 page-faults # 0.160 K/sec ( +- 0.01% )
> 64,747,374,606 cycles # 2.370 GHz ( +- 0.24% ) [33.33%]
> 61,341,580,278 stalled-cycles-frontend # 94.74% frontend cycles idle ( +- 0.26% ) [33.33%]
> 56,702,237,511 stalled-cycles-backend # 87.57% backend cycles idle ( +- 0.07% ) [33.33%]
> 10,033,724,846 instructions # 0.15 insns per cycle
> # 6.11 stalled cycles per insn ( +- 0.09% ) [41.65%]
> 2,190,424,932 branches # 80.195 M/sec ( +- 0.12% ) [41.66%]
> 1,028,630 branch-misses # 0.05% of all branches ( +- 1.50% ) [41.66%]
> 3,302,006,540 L1-dcache-loads
> # 120.891 M/sec ( +- 0.11% ) [41.68%]
> 271,374,358 L1-dcache-misses
> # 8.22% of all L1-dcache hits ( +- 0.04% ) [41.66%]
> 20,385,476 LLC-load
> # 0.746 M/sec ( +- 1.64% ) [33.34%]
> 76,754 LLC-misses
> # 0.38% of all LL-cache hits ( +- 2.35% ) [33.34%]
> 3,309,927,290 dTLB-loads
> # 121.181 M/sec ( +- 0.03% ) [33.34%]
> 2,098,967,427 dTLB-misses
> # 63.41% of all dTLB cache hits ( +- 0.03% ) [33.34%]
>
> 27.364448741 seconds time elapsed ( +- 0.24% )
For this case, the same question as above, thanks in adance. :-)
>
> --------------------------------------------------------------------------
>
> I personally prefer implementation present in this patchset. It doesn't
> touch arch-specific code.
>
>
> Kirill A. Shutemov (10):
> thp: huge zero page: basic preparation
> thp: zap_huge_pmd(): zap huge zero pmd
> thp: copy_huge_pmd(): copy huge zero page
> thp: do_huge_pmd_wp_page(): handle huge zero page
> thp: change_huge_pmd(): keep huge zero page write-protected
> thp: change split_huge_page_pmd() interface
> thp: implement splitting pmd for huge zero page
> thp: setup huge zero page on non-write page fault
> thp: lazy huge zero page allocation
> thp: implement refcounting for huge zero page
>
> Documentation/vm/transhuge.txt | 4 +-
> arch/x86/kernel/vm86_32.c | 2 +-
> fs/proc/task_mmu.c | 2 +-
> include/linux/huge_mm.h | 14 ++-
> include/linux/mm.h | 8 +
> mm/huge_memory.c | 331 +++++++++++++++++++++++++++++++++++++---
> mm/memory.c | 11 +-
> mm/mempolicy.c | 2 +-
> mm/mprotect.c | 2 +-
> mm/mremap.c | 2 +-
> mm/pagewalk.c | 2 +-
> 11 files changed, 334 insertions(+), 46 deletions(-)
>
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