Messages in this thread | | | Date | Mon, 19 Nov 2012 18:20:01 +0800 | From | Jaegeuk Hanse <> | Subject | Re: [PATCH v6 10/12] thp: implement refcounting for huge zero page |
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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@linux.intel.com> >>> >>> 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 /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?
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