From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47187) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z0u2t-00026c-K0 for qemu-devel@nongnu.org; Fri, 05 Jun 2015 12:00:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z0u2s-0006uk-NY for qemu-devel@nongnu.org; Fri, 05 Jun 2015 12:00:35 -0400 Message-ID: <5571C791.2060605@redhat.com> Date: Fri, 05 Jun 2015 18:00:17 +0200 From: Max Reitz MIME-Version: 1.0 References: <5571C5BD.2080804@redhat.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 3/4] docs: document how to configure the qcow2 L2/refcount caches List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alberto Garcia , qemu-devel@nongnu.org Cc: Kevin Wolf , qemu-block@nongnu.org, Stefan Hajnoczi On 05.06.2015 17:56, Alberto Garcia wrote: > On Fri 05 Jun 2015 05:52:29 PM CEST, Max Reitz wrote: >>> +Reducing the memory usage >>> +------------------------- >>> +It is possible to clean unused cache entries in order to reduce the >>> +memory usage during periods of low I/O activity. >>> + >>> +The parameter "cache-clean-interval" defines an interval (in seconds) >>> +after which all unused cache entries are removed from memory. >>> + >>> +This example removes all unused cache entries every 15 minutes: >>> + >>> + -drive file=hd.qcow2,cache-clean-interval=900 >>> + >>> +If unset, the default value for this parameter is 0 and it disables >>> +this feature. >>> + >>> +Note that this functionality currently relies on the MADV_DONTNEED >>> +argument for madvise() to actually free the memory, so it is not >>> +useful in systems that don't follow that behavior. >> I'd like a definition of what "unused" means (I know because of this >> series, but I wouldn't know just from this document). > It means that it hasn't been accessed in that interval (because it was > not needed). Are you thinking of any other possible interpretation? Well... To me, intuitively, "unused" entries in a cache are just empty entries. Just replacing one occurrence of "unused" by "not accessed during the past interval" or something like that would resolve the riddle for me. :-) Max