On 11/19/2012 06:23 PM, Kirill A. Shutemov wrote:
On Mon, Nov 19, 2012 at 06:20:01PM +0800, Jaegeuk Hanse wrote:
On 11/19/2012 05:56 PM, Kirill A. Shutemov wrote:
On Sun, Nov 18, 2012 at 02:23:44PM +0800, Jaegeuk Hanse wrote:
On 11/16/2012 03:27 AM, Kirill A. Shutemov wrote:
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
H. Peter Anvin doesn't like huge zero page which sticks in memory forever
after the first allocation. Here's implementation of lockless refcounting
for huge zero page.
We have two basic primitives: {get,put}_huge_zero_page(). They
manipulate reference counter.
If counter is 0, get_huge_zero_page() allocates a new huge page and
takes two references: one for caller and one for shrinker. We free the
page only in shrinker callback if counter is 1 (only shrinker has the
reference).
put_huge_zero_page() only decrements counter. Counter is never zero
in put_huge_zero_page() since shrinker holds on reference.
Freeing huge zero page in shrinker callback helps to avoid frequent
allocate-free.
Refcounting has cost. On 4 socket machine I observe ~1% slowdown on
parallel (40 processes) read page faulting comparing to lazy huge page
allocation. I think it's pretty reasonable for synthetic benchmark.
Hi Kirill,
I see your and Andew's hot discussion in v4 resend thread.
"I also tried another scenario: usemem -n16 100M -r 1000. It creates
real memory pressure - no easy reclaimable memory. This time
callback called with nr_to_scan > 0 and we freed hzp. "
What's "usemem"? Is it a tool and how to get it?
http://www.spinics.net/lists/linux-mm/attachments/gtarazbJaHPaAT.gtar
Thanks for your response. But how to use it, I even can't compile
the files.
# ./case-lru-file-mmap-read
./case-lru-file-mmap-read: line 3: hw_vars: No such file or directory
./case-lru-file-mmap-read: line 7: 10 * mem / nr_cpu: division by 0
(error token is "nr_cpu")
# gcc usemem.c -o usemem
-lpthread
/tmp/ccFkIDWk.o: In function `do_task':
usemem.c:(.text+0x9f2): undefined reference to `pthread_create'
usemem.c:(.text+0xa44): undefined reference to `pthread_join'
collect2: ld returned 1 exit status
It's hard for me to
find nr_to_scan > 0 in every callset, how can nr_to_scan > 0 in your
scenario?
shrink_slab() calls the callback with nr_to_scan > 0 if system is under
pressure -- look for do_shrinker_shrink().
Why Andrew's example(dd if=/fast-disk/large-file) doesn't call this
path? I think it also can add memory pressure, where I miss?
dd if=large-file only fills pagecache -- easy reclaimable memory.
Pagecache will be dropped first, before shrinking slabs.
How could I confirm page reclaim working hard and slabs are reclaimed at
this time?
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