From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx111.postini.com [74.125.245.111]) by kanga.kvack.org (Postfix) with SMTP id 898FA6B006C for ; Mon, 19 Nov 2012 05:23:12 -0500 (EST) Date: Mon, 19 Nov 2012 12:23:18 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCH v6 10/12] thp: implement refcounting for huge zero page Message-ID: <20121119102318.GA24187@shutemov.name> References: <1353007622-18393-1-git-send-email-kirill.shutemov@linux.intel.com> <1353007622-18393-11-git-send-email-kirill.shutemov@linux.intel.com> <50A87EF0.3060706@gmail.com> <20121119095615.GA23869@otc-wbsnb-06> <50AA07D1.7030906@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50AA07D1.7030906@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jaegeuk Hanse Cc: "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , linux-mm@kvack.org, Andi Kleen , "H. Peter Anvin" , linux-kernel@vger.kernel.org, David Rientjes 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" > >>> > >>>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. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org