Re: [RFC v7 00/11] Support vrange for anonymous page
From: KOSAKI Motohiro
Date: Wed Apr 10 2013 - 16:23:10 EST
(3/12/13 3:38 AM), Minchan Kim wrote:
> First of all, let's define the term.
> From now on, I'd like to call it as vrange(a.k.a volatile range)
> for anonymous page. If you have a better name in mind, please suggest.
>
> This version is still *RFC* because it's just quick prototype so
> it doesn't support THP/HugeTLB/KSM and even couldn't build on !x86.
> Before further sorting out issues, I'd like to post current direction
> and discuss it. Of course, I'd like to extend this discussion in
> comming LSF/MM.
>
> In this version, I changed lots of thing, expecially removed vma-based
> approach because it needs write-side lock for mmap_sem, which will drop
> performance in mutli-threaded big SMP system, KOSAKI pointed out.
> And vma-based approach is hard to meet requirement of new system call by
> John Stultz's suggested semantic for consistent purged handling.
> (http://linux-kernel.2935.n7.nabble.com/RFC-v5-0-8-Support-volatile-for-anonymous-range-tt575773.html#none)
>
> I tested this patchset with modified jemalloc allocator which was
> leaded by Jason Evans(jemalloc author) who was interest in this feature
> and was happy to port his allocator to use new system call.
> Super Thanks Jason!
>
> The benchmark for test is ebizzy. It have been used for testing the
> allocator performance so it's good for me. Again, thanks for recommending
> the benchmark, Jason.
> (http://people.freebsd.org/~kris/scaling/ebizzy.html)
>
> The result is good on my machine (12 CPU, 1.2GHz, DRAM 2G)
>
> ebizzy -S 20
>
> jemalloc-vanilla: 52389 records/sec
> jemalloc-vrange: 203414 records/sec
>
> ebizzy -S 20 with background memory pressure
>
> jemalloc-vanilla: 40746 records/sec
> jemalloc-vrange: 174910 records/sec
>
> And it's much improved on KVM virtual machine.
>
> This patchset is based on v3.9-rc2
>
> - What's the sys_vrange(addr, length, mode, behavior)?
>
> It's a hint that user deliver to kernel so kernel can *discard*
> pages in a range anytime. mode is one of VRANGE_VOLATILE and
> VRANGE_NOVOLATILE. VRANGE_NOVOLATILE is memory pin operation so
> kernel coudn't discard any pages any more while VRANGE_VOLATILE
> is memory unpin opeartion so kernel can discard pages in vrange
> anytime. At a moment, behavior is one of VRANGE_FULL and VRANGE
> PARTIAL. VRANGE_FULL tell kernel that once kernel decide to
> discard page in a vrange, please, discard all of pages in a
> vrange selected by victim vrange. VRANGE_PARTIAL tell kernel
> that please discard of some pages in a vrange. But now I didn't
> implemented VRANGE_PARTIAL handling yet.
>
> - What happens if user access page(ie, virtual address) discarded
> by kernel?
>
> The user can encounter SIGBUS.
>
> - What should user do for avoding SIGBUS?
> He should call vrange(addr, length, VRANGE_NOVOLATILE, mode) before
> accessing the range which was called
> vrange(addr, length, VRANGE_VOLATILE, mode)
>
> - What happens if user access page(ie, virtual address) doesn't
> discarded by kernel?
>
> The user can see vaild data which was there before calling
> vrange(., VRANGE_VOLATILE) without page fault.
>
> - What's different with madvise(DONTNEED)?
>
> System call semantic
>
> DONTNEED makes sure user always can see zero-fill pages after
> he calls madvise while vrange can see data or encounter SIGBUS.
For replacing DONTNEED, user want to zero-fill pages like DONTNEED
instead of SIGBUS. So, new flag option would be nice.
I played a bit this patch. The result looks really promissing.
(i.e. 20x faster)
My machine have 24cpus, 8GB ram, kvm guest. I guess current DONTNEED
implementation doesn't fit kvm at all.
# of # of # of
thread iter iter (patched glibc)
----------------------------------
1 438 10740
2 842 20916
4 987 32534
8 717 15155
12 714 14109
16 708 13457
20 720 13742
24 727 13642
28 715 13328
32 709 13096
36 705 13661
40 708 13634
44 707 13367
48 714 13377
---------libc patch (just dirty hack) ----------------------
diff --git a/malloc/arena.c b/malloc/arena.c
index 12a48ad..da04f67 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -365,6 +365,8 @@ extern struct dl_open_hook *_dl_open_hook;
libc_hidden_proto (_dl_open_hook);
#endif
+int vrange_enabled = 0;
+
static void
ptmalloc_init (void)
{
@@ -457,6 +459,18 @@ ptmalloc_init (void)
if (check_action != 0)
__malloc_check_init();
}
+
+ {
+ char *vrange = getenv("MALLOC_VRANGE");
+ if (vrange) {
+ int val = atoi(vrange);
+ if (val) {
+ printf("glibc: vrange enabled\n");
+ vrange_enabled = !!val;
+ }
+ }
+ }
+
void (*hook) (void) = force_reg (__malloc_initialize_hook);
if (hook != NULL)
(*hook)();
@@ -628,9 +642,14 @@ shrink_heap(heap_info *h, long diff)
return -2;
h->mprotect_size = new_size;
}
- else
- __madvise ((char *)h + new_size, diff, MADV_DONTNEED);
+ else {
+ if (vrange_enabled) {
+ syscall(314, (char *)h + new_size, diff, 0, 1);
+ } else {
+ __madvise ((char *)h + new_size, diff, MADV_DONTNEED);
+ }
/*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/
+ }
h->size = new_size;
return 0;
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 70b9329..3782244 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -4403,6 +4403,7 @@ _int_pvalloc(mstate av, size_t bytes)
/*
------------------------------ malloc_trim ------------------------------
*/
+extern int vrange_enabled;
static int mtrim(mstate av, size_t pad)
{
@@ -4443,7 +4444,12 @@ static int mtrim(mstate av, size_t pad)
content. */
memset (paligned_mem, 0x89, size & ~psm1);
#endif
- __madvise (paligned_mem, size & ~psm1, MADV_DONTNEED);
+
+ if (vrange_enabled) {
+ syscall(314, paligned_mem, size & ~psm1, 0, 1);
+ } else {
+ __madvise (paligned_mem, size & ~psm1, MADV_DONTNEED);
+ }
result = 1;
}
(END)
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