linux-toradex.git/mm/huge_memory.c, branch v3.2.3

thp: reduce khugepaged freezing latency

2011-12-09T15:50:28+00:00

khugepaged can sometimes cause suspend to fail, requiring that the user
retry the suspend operation.

Use wait_event_freezable_timeout() instead of
schedule_timeout_interruptible() to avoid missing freezer wakeups.  A
try_to_freeze() would have been needed in the khugepaged_alloc_hugepage
tight loop too in case of the allocation failing repeatedly, and
wait_event_freezable_timeout will provide it too.

khugepaged would still freeze just fine by trying again the next minute
but it's better if it freezes immediately.

Reported-by: Jiri Slaby 
Signed-off-by: Andrea Arcangeli 
Tested-by: Jiri Slaby 
Cc: Tejun Heo 
Cc: Oleg Nesterov 
Cc: "Srivatsa S. Bhat" 
Cc: "Rafael J. Wysocki" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: thp: tail page refcounting fix

2011-11-02T23:06:57+00:00

Michel while working on the working set estimation code, noticed that
calling get_page_unless_zero() on a random pfn_to_page(random_pfn)
wasn't safe, if the pfn ended up being a tail page of a transparent
hugepage under splitting by __split_huge_page_refcount().

He then found the problem could also theoretically materialize with
page_cache_get_speculative() during the speculative radix tree lookups
that uses get_page_unless_zero() in SMP if the radix tree page is freed
and reallocated and get_user_pages is called on it before
page_cache_get_speculative has a chance to call get_page_unless_zero().

So the best way to fix the problem is to keep page_tail->_count zero at
all times.  This will guarantee that get_page_unless_zero() can never
succeed on any tail page.  page_tail->_mapcount is guaranteed zero and
is unused for all tail pages of a compound page, so we can simply
account the tail page references there and transfer them to
tail_page->_count in __split_huge_page_refcount() (in addition to the
head_page->_mapcount).

While debugging this s/_count/_mapcount/ change I also noticed get_page is
called by direct-io.c on pages returned by get_user_pages.  That wasn't
entirely safe because the two atomic_inc in get_page weren't atomic.  As
opposed to other get_user_page users like secondary-MMU page fault to
establish the shadow pagetables would never call any superflous get_page
after get_user_page returns.  It's safer to make get_page universally safe
for tail pages and to use get_page_foll() within follow_page (inside
get_user_pages()).  get_page_foll() is safe to do the refcounting for tail
pages without taking any locks because it is run within PT lock protected
critical sections (PT lock for pte and page_table_lock for
pmd_trans_huge).

The standard get_page() as invoked by direct-io instead will now take
the compound_lock but still only for tail pages.  The direct-io paths
are usually I/O bound and the compound_lock is per THP so very
finegrined, so there's no risk of scalability issues with it.  A simple
direct-io benchmarks with all lockdep prove locking and spinlock
debugging infrastructure enabled shows identical performance and no
overhead.  So it's worth it.  Ideally direct-io should stop calling
get_page() on pages returned by get_user_pages().  The spinlock in
get_page() is already optimized away for no-THP builds but doing
get_page() on tail pages returned by GUP is generally a rare operation
and usually only run in I/O paths.

This new refcounting on page_tail->_mapcount in addition to avoiding new
RCU critical sections will also allow the working set estimation code to
work without any further complexity associated to the tail page
refcounting with THP.

Signed-off-by: Andrea Arcangeli 
Reported-by: Michel Lespinasse 
Reviewed-by: Michel Lespinasse 
Reviewed-by: Minchan Kim 
Cc: Peter Zijlstra 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Rik van Riel 
Cc: Mel Gorman 
Cc: KOSAKI Motohiro 
Cc: Benjamin Herrenschmidt 
Cc: David Gibson 
Cc: 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/huge_memory: fix typo when updating mmu cache

2011-11-01T00:30:51+00:00

There are three cases of update_mmu_cache() in the file, and the case in
function collapse_huge_page() has a typo, namely the last parameter used,
which is corrected based on the other two cases.

Due to the define of update_mmu_cache by X86, the only arch that
implements THP currently, the change here has no really crystal point, but
one or two minutes of efforts could be saved for those archs that are
likely to support THP in future.

Signed-off-by: Hillf Danton 
Cc: Johannes Weiner 
Reviewed-by: Andrea Arcangeli 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/huge_memory: fix copying user highpage

2011-11-01T00:30:50+00:00

The THP copy-on-write handler falls back to regular-sized pages for a huge
page replacement upon allocation failure or if THP has been individually
disabled in the target VMA.  The loop responsible for copying page-sized
chunks accidentally uses multiples of PAGE_SHIFT instead of PAGE_SIZE as
the virtual address arg for copy_user_highpage().

Signed-off-by: Hillf Danton 
Acked-by: Johannes Weiner 
Reviewed-by: Andrea Arcangeli 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/huge_memory.c: quiet sparse noise

2011-11-01T00:30:50+00:00

Quiet the sparse noise:

warning: symbol 'khugepaged_scan' was not declared. Should it be static?
warning: context imbalance in 'khugepaged_scan_mm_slot' - unexpected unlock

Signed-off-by: H Hartley Sweeten 
Cc: Andrea Arcangeli 
Cc: Rik van Riel 
Cc: Johannes Weiner 
Cc: KAMEZAWA Hiroyuki 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

thp: mremap support and TLB optimization

2011-11-01T00:30:48+00:00

This adds THP support to mremap (decreases the number of split_huge_page()
calls).

Here are also some benchmarks with a proggy like this:

===
#define _GNU_SOURCE
#include 
#include 
#include 
#include 
#include 

#define SIZE (5UL*1024*1024*1024)

int main()
{
        static struct timeval oldstamp, newstamp;
	long diffsec;
	char *p, *p2, *p3, *p4;
	if (posix_memalign((void **)&p, 2*1024*1024, SIZE))
		perror("memalign"), exit(1);
	if (posix_memalign((void **)&p2, 2*1024*1024, SIZE))
		perror("memalign"), exit(1);
	if (posix_memalign((void **)&p3, 2*1024*1024, 4096))
		perror("memalign"), exit(1);

	memset(p, 0xff, SIZE);
	memset(p2, 0xff, SIZE);
	memset(p3, 0x77, 4096);
	gettimeofday(&oldstamp, NULL);
	p4 = mremap(p, SIZE, SIZE, MREMAP_FIXED|MREMAP_MAYMOVE, p3);
	gettimeofday(&newstamp, NULL);
	diffsec = newstamp.tv_sec - oldstamp.tv_sec;
	diffsec = newstamp.tv_usec - oldstamp.tv_usec + 1000000 * diffsec;
	printf("usec %ld\n", diffsec);
	if (p == MAP_FAILED || p4 != p3)
	//if (p == MAP_FAILED)
		perror("mremap"), exit(1);
	if (memcmp(p4, p2, SIZE))
		printf("mremap bug\n"), exit(1);
	printf("ok\n");

	return 0;
}
===

THP on

 Performance counter stats for './largepage13' (3 runs):

          69195836 dTLB-loads                 ( +-   3.546% )  (scaled from 50.30%)
             60708 dTLB-load-misses           ( +-  11.776% )  (scaled from 52.62%)
         676266476 dTLB-stores                ( +-   5.654% )  (scaled from 69.54%)
             29856 dTLB-store-misses          ( +-   4.081% )  (scaled from 89.22%)
        1055848782 iTLB-loads                 ( +-   4.526% )  (scaled from 80.18%)
              8689 iTLB-load-misses           ( +-   2.987% )  (scaled from 58.20%)

        7.314454164  seconds time elapsed   ( +-   0.023% )

THP off

 Performance counter stats for './largepage13' (3 runs):

        1967379311 dTLB-loads                 ( +-   0.506% )  (scaled from 60.59%)
           9238687 dTLB-load-misses           ( +-  22.547% )  (scaled from 61.87%)
        2014239444 dTLB-stores                ( +-   0.692% )  (scaled from 60.40%)
           3312335 dTLB-store-misses          ( +-   7.304% )  (scaled from 67.60%)
        6764372065 iTLB-loads                 ( +-   0.925% )  (scaled from 79.00%)
              8202 iTLB-load-misses           ( +-   0.475% )  (scaled from 70.55%)

        9.693655243  seconds time elapsed   ( +-   0.069% )

grep thp /proc/vmstat
thp_fault_alloc 35849
thp_fault_fallback 0
thp_collapse_alloc 3
thp_collapse_alloc_failed 0
thp_split 0

thp_split 0 confirms no thp split despite plenty of hugepages allocated.

The measurement of only the mremap time (so excluding the 3 long
memset and final long 10GB memory accessing memcmp):

THP on

usec 14824
usec 14862
usec 14859

THP off

usec 256416
usec 255981
usec 255847

With an older kernel without the mremap optimizations (the below patch
optimizes the non THP version too).

THP on

usec 392107
usec 390237
usec 404124

THP off

usec 444294
usec 445237
usec 445820

I guess with a threaded program that sends more IPI on large SMP it'd
create an even larger difference.

All debug options are off except DEBUG_VM to avoid skewing the
results.

The only problem for native 2M mremap like it happens above both the
source and destination address must be 2M aligned or the hugepmd can't be
moved without a split but that is an hardware limitation.

[akpm@linux-foundation.org: coding-style nitpicking]
Signed-off-by: Andrea Arcangeli 
Acked-by: Johannes Weiner 
Acked-by: Mel Gorman 
Acked-by: Rik van Riel 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/huge_memory.c: minor lock simplification in __khugepaged_exit

2011-07-26T03:57:09+00:00

The lock is released first thing in all three branches.  Simplify this by
unconditionally releasing lock and remove else clause which was only there
to be sure lock was released.

Signed-off-by: Chris Wright 
Reviewed-by: Michal Hocko 
Cc: Andrea Arcangeli 
Acked-by: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: remove khugepaged double thp vmstat update with CONFIG_NUMA=n

2011-06-16T03:03:58+00:00

Johannes noticed the vmstat update is already taken care of by
khugepaged_alloc_hugepage() internally.  The only places that are required
to update the vmstat are the callers of alloc_hugepage (callers of
khugepaged_alloc_hugepage aren't).

Signed-off-by: Andrea Arcangeli 
Reported-by: Johannes Weiner 
Acked-by: Rik van Riel 
Reviewed-by: Minchan Kim 
Acked-by: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: thp: optimize memcg charge in khugepaged

2011-05-25T15:39:21+00:00

We don't need to hold the mmmap_sem through mem_cgroup_newpage_charge(),
the mmap_sem is only hold for keeping the vma stable and we don't need the
vma stable anymore after we return from alloc_hugepage_vma().

Signed-off-by: Andrea Arcangeli 
Cc: Johannes Weiner 
Cc: Hugh Dickins 
Cc: David Rientjes 
Cc: Minchan Kim 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: convert anon_vma->lock to a mutex

2011-05-25T15:39:19+00:00

Straightforward conversion of anon_vma->lock to a mutex.

Signed-off-by: Peter Zijlstra 
Acked-by: Hugh Dickins 
Reviewed-by: KOSAKI Motohiro 
Cc: Benjamin Herrenschmidt 
Cc: David Miller 
Cc: Martin Schwidefsky 
Cc: Russell King 
Cc: Paul Mundt 
Cc: Jeff Dike 
Cc: Richard Weinberger 
Cc: Tony Luck 
Cc: KAMEZAWA Hiroyuki 
Cc: Mel Gorman 
Cc: Nick Piggin 
Cc: Namhyung Kim 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds