> From: Wanpeng Li [mailto:liw...@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; Konrad > Rzeszutek Wilk; Minchan > Kim; linux...@kvack.org; linux-kernel@vger.kernel.org > Subject: Re: [PATCH 4/4] zcache: add pageframes count once compress > zero-filled pages twice > > On Wed, Mar 13, 2013 at 09:42:16AM -0700, Dan Magenheimer wrote: > >> From: Wanpeng Li [mailto:liw...@linux.vnet.ibm.com] > >> Sent: Wednesday, March 13, 2013 1:05 AM > >> To: Andrew Morton > >> Cc: Greg Kroah-Hartman; Dan Magenheimer; Seth Jennings; Konrad Rzeszutek > >> Wilk; Minchan Kim; linux- > >> m...@kvack.org; linux-kernel@vger.kernel.org; Wanpeng Li > >> Subject: [PATCH 4/4] zcache: add pageframes count once compress > >> zero-filled 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 compression > >> contribute to one [eph|pers]pageframe count accumulated. > > > > Hi Dan, > > >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. > > > > 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 == 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
