From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id 1B3BB6B0027 for ; Thu, 14 Mar 2013 12:11:24 -0400 (EDT) MIME-Version: 1.0 Message-ID: Date: Thu, 14 Mar 2013 09:10:48 -0700 (PDT) From: Dan Magenheimer Subject: RE: [PATCH 4/4] zcache: add pageframes count once compress zero-filled pages twice References: <1363158321-20790-1-git-send-email-liwanp@linux.vnet.ibm.com> <1363158321-20790-5-git-send-email-liwanp@linux.vnet.ibm.com> <634487ea-fbbd-4eb9-9a18-9206edc4e0d2@default> <20130314002056.GA10062@hacker.(null)> In-Reply-To: <20130314002056.GA10062@hacker.(null)> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Wanpeng Li Cc: Andrew Morton , Greg Kroah-Hartman , Seth Jennings , Konrad Rzeszutek Wilk , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org > From: Wanpeng Li [mailto:liwanp@linux.vnet.ibm.com] > Sent: Wednesday, March 13, 2013 6:21 PM > To: Dan Magenheimer > Cc: Andrew Morton; Greg Kroah-Hartman; Dan Magenheimer; Seth Jennings; Ko= nrad Rzeszutek Wilk; Minchan > Kim; linux-mm@kvack.org; linux-kernel@vger.kernel.org > Subject: Re: [PATCH 4/4] zcache: add pageframes count once compress zero-= filled pages twice >=20 > On Wed, Mar 13, 2013 at 09:42:16AM -0700, Dan Magenheimer wrote: > >> From: Wanpeng Li [mailto:liwanp@linux.vnet.ibm.com] > >> Sent: Wednesday, March 13, 2013 1:05 AM > >> To: Andrew Morton > >> Cc: Greg Kroah-Hartman; Dan Magenheimer; Seth Jennings; Konrad Rzeszut= ek Wilk; Minchan Kim; linux- > >> mm@kvack.org; linux-kernel@vger.kernel.org; Wanpeng Li > >> Subject: [PATCH 4/4] zcache: add pageframes count once compress zero-f= illed pages twice > > > >Hi Wanpeng -- > > > >Thanks for taking on this task from the drivers/staging/zcache TODO list= ! > > > >> Since zbudpage consist of two zpages, two zero-filled pages compressio= n > >> contribute to one [eph|pers]pageframe count accumulated. > > >=20 > Hi Dan, >=20 > >I'm not sure why this is necessary. The [eph|pers]pageframe count > >is supposed to be counting actual pageframes used by zcache. Since > >your patch eliminates the need to store zero pages, no pageframes > >are needed at all to store zero pages, so it's not necessary > >to increment zcache_[eph|pers]_pageframes when storing zero > >pages. > > >=20 > Great point! It seems that we also don't need to caculate > zcache_[eph|pers]_zpages for zero-filled pages. I will fix > it in next version. :-) Hi Wanpeng -- I think we DO need to increment/decrement zcache_[eph|pers]_zpages for zero-filled pages. The main point of the counters for zpages and pageframes is to be able to calculate density =3D=3D zpages/pageframes. A zero-filled page becomes a zpage that "compresses" to zero bytes and, as a result, requires zero pageframes for storage. So the zpages counter should be increased but the pageframes counter should not. If you are changing the patch anyway, I do like better the use of "zero_filled_page" rather than just "zero" or "zero page". So it might be good to change: handle_zero_page -> handle_zero_filled_page pages_zero -> zero_filled_pages zcache_pages_zero -> zcache_zero_filled_pages and maybe page_zero_filled -> page_is_zero_filled Thanks, Dan -- 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