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authorMinchan Kim <minchan@kernel.org>2016-01-15 16:54:53 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-15 17:56:32 -0800
commit854e9ed09dedf0c19ac8640e91bcc74bc3f9e5c9 (patch)
tree4abd01fcd0378a3b3e39fb1c2de028b4076507ef /mm/madvise.c
parent17ec4cd985780a7e30aa45bb8f272237c12502a4 (diff)
downloadlinux-854e9ed09dedf0c19ac8640e91bcc74bc3f9e5c9.tar.bz2
mm: support madvise(MADV_FREE)
Linux doesn't have an ability to free pages lazy while other OS already have been supported that named by madvise(MADV_FREE). The gain is clear that kernel can discard freed pages rather than swapping out or OOM if memory pressure happens. Without memory pressure, freed pages would be reused by userspace without another additional overhead(ex, page fault + allocation + zeroing). Jason Evans said: : Facebook has been using MAP_UNINITIALIZED : (https://lkml.org/lkml/2012/1/18/308) in some of its applications for : several years, but there are operational costs to maintaining this : out-of-tree in our kernel and in jemalloc, and we are anxious to retire it : in favor of MADV_FREE. When we first enabled MAP_UNINITIALIZED it : increased throughput for much of our workload by ~5%, and although the : benefit has decreased using newer hardware and kernels, there is still : enough benefit that we cannot reasonably retire it without a replacement. : : Aside from Facebook operations, there are numerous broadly used : applications that would benefit from MADV_FREE. The ones that immediately : come to mind are redis, varnish, and MariaDB. I don't have much insight : into Android internals and development process, but I would hope to see : MADV_FREE support eventually end up there as well to benefit applications : linked with the integrated jemalloc. : : jemalloc will use MADV_FREE once it becomes available in the Linux kernel. : In fact, jemalloc already uses MADV_FREE or equivalent everywhere it's : available: *BSD, OS X, Windows, and Solaris -- every platform except Linux : (and AIX, but I'm not sure it even compiles on AIX). The lack of : MADV_FREE on Linux forced me down a long series of increasingly : sophisticated heuristics for madvise() volume reduction, and even so this : remains a common performance issue for people using jemalloc on Linux. : Please integrate MADV_FREE; many people will benefit substantially. How it works: When madvise syscall is called, VM clears dirty bit of ptes of the range. If memory pressure happens, VM checks dirty bit of page table and if it found still "clean", it means it's a "lazyfree pages" so VM could discard the page instead of swapping out. Once there was store operation for the page before VM peek a page to reclaim, dirty bit is set so VM can swap out the page instead of discarding. One thing we should notice is that basically, MADV_FREE relies on dirty bit in page table entry to decide whether VM allows to discard the page or not. IOW, if page table entry includes marked dirty bit, VM shouldn't discard the page. However, as a example, if swap-in by read fault happens, page table entry doesn't have dirty bit so MADV_FREE could discard the page wrongly. For avoiding the problem, MADV_FREE did more checks with PageDirty and PageSwapCache. It worked out because swapped-in page lives on swap cache and since it is evicted from the swap cache, the page has PG_dirty flag. So both page flags check effectively prevent wrong discarding by MADV_FREE. However, a problem in above logic is that swapped-in page has PG_dirty still after they are removed from swap cache so VM cannot consider the page as freeable any more even if madvise_free is called in future. Look at below example for detail. ptr = malloc(); memset(ptr); .. .. .. heavy memory pressure so all of pages are swapped out .. .. var = *ptr; -> a page swapped-in and could be removed from swapcache. Then, page table doesn't mark dirty bit and page descriptor includes PG_dirty .. .. madvise_free(ptr); -> It doesn't clear PG_dirty of the page. .. .. .. .. heavy memory pressure again. .. In this time, VM cannot discard the page because the page .. has *PG_dirty* To solve the problem, this patch clears PG_dirty if only the page is owned exclusively by current process when madvise is called because PG_dirty represents ptes's dirtiness in several processes so we could clear it only if we own it exclusively. Firstly, heavy users would be general allocators(ex, jemalloc, tcmalloc and hope glibc supports it) and jemalloc/tcmalloc already have supported the feature for other OS(ex, FreeBSD) barrios@blaptop:~/benchmark/ebizzy$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 12 On-line CPU(s) list: 0-11 Thread(s) per core: 1 Core(s) per socket: 1 Socket(s): 12 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 2 Stepping: 3 CPU MHz: 3200.185 BogoMIPS: 6400.53 Virtualization: VT-x Hypervisor vendor: KVM Virtualization type: full L1d cache: 32K L1i cache: 32K L2 cache: 4096K NUMA node0 CPU(s): 0-11 ebizzy benchmark(./ebizzy -S 10 -n 512) Higher avg is better. vanilla-jemalloc MADV_free-jemalloc 1 thread records: 10 records: 10 avg: 2961.90 avg: 12069.70 std: 71.96(2.43%) std: 186.68(1.55%) max: 3070.00 max: 12385.00 min: 2796.00 min: 11746.00 2 thread records: 10 records: 10 avg: 5020.00 avg: 17827.00 std: 264.87(5.28%) std: 358.52(2.01%) max: 5244.00 max: 18760.00 min: 4251.00 min: 17382.00 4 thread records: 10 records: 10 avg: 8988.80 avg: 27930.80 std: 1175.33(13.08%) std: 3317.33(11.88%) max: 9508.00 max: 30879.00 min: 5477.00 min: 21024.00 8 thread records: 10 records: 10 avg: 13036.50 avg: 33739.40 std: 170.67(1.31%) std: 5146.22(15.25%) max: 13371.00 max: 40572.00 min: 12785.00 min: 24088.00 16 thread records: 10 records: 10 avg: 11092.40 avg: 31424.20 std: 710.60(6.41%) std: 3763.89(11.98%) max: 12446.00 max: 36635.00 min: 9949.00 min: 25669.00 32 thread records: 10 records: 10 avg: 11067.00 avg: 34495.80 std: 971.06(8.77%) std: 2721.36(7.89%) max: 12010.00 max: 38598.00 min: 9002.00 min: 30636.00 In summary, MADV_FREE is about much faster than MADV_DONTNEED. This patch (of 12): Add core MADV_FREE implementation. [akpm@linux-foundation.org: small cleanups] Signed-off-by: Minchan Kim <minchan@kernel.org> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Mika Penttil <mika.penttila@nextfour.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Jason Evans <je@fb.com> Cc: Daniel Micay <danielmicay@gmail.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Shaohua Li <shli@kernel.org> Cc: <yalin.wang2010@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: "James E.J. Bottomley" <jejb@parisc-linux.org> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: "Shaohua Li" <shli@kernel.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Chen Gang <gang.chen.5i5j@gmail.com> Cc: Chris Zankel <chris@zankel.net> Cc: Darrick J. Wong <darrick.wong@oracle.com> Cc: David S. Miller <davem@davemloft.net> Cc: Helge Deller <deller@gmx.de> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Richard Henderson <rth@twiddle.net> Cc: Roland Dreier <roland@kernel.org> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Shaohua Li <shli@kernel.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/madvise.c')
-rw-r--r--mm/madvise.c170
1 files changed, 170 insertions, 0 deletions
diff --git a/mm/madvise.c b/mm/madvise.c
index c889fcbb530e..ed137fde4459 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -20,6 +20,9 @@
#include <linux/backing-dev.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <linux/mmu_notifier.h>
+
+#include <asm/tlb.h>
/*
* Any behaviour which results in changes to the vma->vm_flags needs to
@@ -32,6 +35,7 @@ static int madvise_need_mmap_write(int behavior)
case MADV_REMOVE:
case MADV_WILLNEED:
case MADV_DONTNEED:
+ case MADV_FREE:
return 0;
default:
/* be safe, default to 1. list exceptions explicitly */
@@ -256,6 +260,163 @@ static long madvise_willneed(struct vm_area_struct *vma,
return 0;
}
+static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
+ unsigned long end, struct mm_walk *walk)
+
+{
+ struct mmu_gather *tlb = walk->private;
+ struct mm_struct *mm = tlb->mm;
+ struct vm_area_struct *vma = walk->vma;
+ spinlock_t *ptl;
+ pte_t *orig_pte, *pte, ptent;
+ struct page *page;
+
+ split_huge_pmd(vma, pmd, addr);
+ if (pmd_trans_unstable(pmd))
+ return 0;
+
+ orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ arch_enter_lazy_mmu_mode();
+ for (; addr != end; pte++, addr += PAGE_SIZE) {
+ ptent = *pte;
+
+ if (!pte_present(ptent))
+ continue;
+
+ page = vm_normal_page(vma, addr, ptent);
+ if (!page)
+ continue;
+
+ /*
+ * If pmd isn't transhuge but the page is THP and
+ * is owned by only this process, split it and
+ * deactivate all pages.
+ */
+ if (PageTransCompound(page)) {
+ if (page_mapcount(page) != 1)
+ goto out;
+ get_page(page);
+ if (!trylock_page(page)) {
+ put_page(page);
+ goto out;
+ }
+ pte_unmap_unlock(orig_pte, ptl);
+ if (split_huge_page(page)) {
+ unlock_page(page);
+ put_page(page);
+ pte_offset_map_lock(mm, pmd, addr, &ptl);
+ goto out;
+ }
+ put_page(page);
+ unlock_page(page);
+ pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ pte--;
+ addr -= PAGE_SIZE;
+ continue;
+ }
+
+ VM_BUG_ON_PAGE(PageTransCompound(page), page);
+
+ if (PageSwapCache(page) || PageDirty(page)) {
+ if (!trylock_page(page))
+ continue;
+ /*
+ * If page is shared with others, we couldn't clear
+ * PG_dirty of the page.
+ */
+ if (page_mapcount(page) != 1) {
+ unlock_page(page);
+ continue;
+ }
+
+ if (PageSwapCache(page) && !try_to_free_swap(page)) {
+ unlock_page(page);
+ continue;
+ }
+
+ ClearPageDirty(page);
+ unlock_page(page);
+ }
+
+ if (pte_young(ptent) || pte_dirty(ptent)) {
+ /*
+ * Some of architecture(ex, PPC) don't update TLB
+ * with set_pte_at and tlb_remove_tlb_entry so for
+ * the portability, remap the pte with old|clean
+ * after pte clearing.
+ */
+ ptent = ptep_get_and_clear_full(mm, addr, pte,
+ tlb->fullmm);
+
+ ptent = pte_mkold(ptent);
+ ptent = pte_mkclean(ptent);
+ set_pte_at(mm, addr, pte, ptent);
+ tlb_remove_tlb_entry(tlb, pte, addr);
+ }
+ }
+out:
+ arch_leave_lazy_mmu_mode();
+ pte_unmap_unlock(orig_pte, ptl);
+ cond_resched();
+ return 0;
+}
+
+static void madvise_free_page_range(struct mmu_gather *tlb,
+ struct vm_area_struct *vma,
+ unsigned long addr, unsigned long end)
+{
+ struct mm_walk free_walk = {
+ .pmd_entry = madvise_free_pte_range,
+ .mm = vma->vm_mm,
+ .private = tlb,
+ };
+
+ tlb_start_vma(tlb, vma);
+ walk_page_range(addr, end, &free_walk);
+ tlb_end_vma(tlb, vma);
+}
+
+static int madvise_free_single_vma(struct vm_area_struct *vma,
+ unsigned long start_addr, unsigned long end_addr)
+{
+ unsigned long start, end;
+ struct mm_struct *mm = vma->vm_mm;
+ struct mmu_gather tlb;
+
+ if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
+ return -EINVAL;
+
+ /* MADV_FREE works for only anon vma at the moment */
+ if (!vma_is_anonymous(vma))
+ return -EINVAL;
+
+ start = max(vma->vm_start, start_addr);
+ if (start >= vma->vm_end)
+ return -EINVAL;
+ end = min(vma->vm_end, end_addr);
+ if (end <= vma->vm_start)
+ return -EINVAL;
+
+ lru_add_drain();
+ tlb_gather_mmu(&tlb, mm, start, end);
+ update_hiwater_rss(mm);
+
+ mmu_notifier_invalidate_range_start(mm, start, end);
+ madvise_free_page_range(&tlb, vma, start, end);
+ mmu_notifier_invalidate_range_end(mm, start, end);
+ tlb_finish_mmu(&tlb, start, end);
+
+ return 0;
+}
+
+static long madvise_free(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ *prev = vma;
+ return madvise_free_single_vma(vma, start, end);
+}
+
/*
* Application no longer needs these pages. If the pages are dirty,
* it's OK to just throw them away. The app will be more careful about
@@ -379,6 +540,14 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
return madvise_remove(vma, prev, start, end);
case MADV_WILLNEED:
return madvise_willneed(vma, prev, start, end);
+ case MADV_FREE:
+ /*
+ * XXX: In this implementation, MADV_FREE works like
+ * MADV_DONTNEED on swapless system or full swap.
+ */
+ if (get_nr_swap_pages() > 0)
+ return madvise_free(vma, prev, start, end);
+ /* passthrough */
case MADV_DONTNEED:
return madvise_dontneed(vma, prev, start, end);
default:
@@ -398,6 +567,7 @@ madvise_behavior_valid(int behavior)
case MADV_REMOVE:
case MADV_WILLNEED:
case MADV_DONTNEED:
+ case MADV_FREE:
#ifdef CONFIG_KSM
case MADV_MERGEABLE:
case MADV_UNMERGEABLE: