Date: Wed, 23 Jun 2010 23:48:03 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Alexander Leidinger <Alexander@Leidinger.net> Cc: freebsd-fs@FreeBSD.org, alc@FreeBSD.org, fs@FreeBSD.org, pho@FreeBSD.org Subject: Re: Tmpfs elimination of double-copy Message-ID: <20100623233917.N45555@delplex.bde.org> In-Reply-To: <20100622103001.12481jemueuswkn4@webmail.leidinger.net> References: <20100621125825.GG13238@deviant.kiev.zoral.com.ua> <201006211030.55327.jhb@freebsd.org> <20100621184928.GI13238@deviant.kiev.zoral.com.ua> <20100622091340.25034svc6uz3k4g0@webmail.leidinger.net> <20100622081005.GQ13238@deviant.kiev.zoral.com.ua> <20100622103001.12481jemueuswkn4@webmail.leidinger.net>
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On Tue, 22 Jun 2010, Alexander Leidinger wrote: > Quoting Kostik Belousov <kostikbel@gmail.com> (from Tue, 22 Jun 2010 11:10:05 > +0300): > >> On Tue, Jun 22, 2010 at 09:13:40AM +0200, Alexander Leidinger wrote: > >>> Did you measure the performance before/after? If not, what are your >>> performance expectations? I don't expect we get double the >>> performance, but if every data of a write is copied twice, I would >>> guess there is a measurable benefit. >> No, I did not bothered. Real benefit of the change is the memory saving. > > For me the real benefit is that it survives a fsx run now. Anyone can buy > more money and faster machines, but stability... It's not so easy to buy machines enough faster to compensate from thrashing of caches caused by extra memory accesses. > This does not mean I do not appreciate the memory saving (when the change > hits one of my machines, I may decide to use tmpfs in places where I didn't > use it before because of memory size concerns). > > That being said, I'm sure that mentioning the performance aspect additionally > to the fsx and memory parts may be good in the release notes (and/or a > blog/whatever post of someone). How much performance does it give anyway? I would guess a negative amount compared with a an async mounted ffs, at least if it double buffers everything, since the double buffering would halve the amount of memory available for caching files. Bruce
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