Date: Mon, 28 Mar 2005 23:11:48 -0500 (EST) From: Jeff Roberson <jroberson@chesapeake.net> To: Stephan Uphoff <ups@tree.com> Cc: arch@freebsd.org Subject: Re: Freeing vnodes. Message-ID: <20050328231118.R54623@mail.chesapeake.net> In-Reply-To: <1111983665.64310.19.camel@palm> References: <20050314213038.V20708@mail.chesapeake.net> <1110856553.29804.37784.camel@palm> <1110896909.29804.39143.camel@palm> <1111983665.64310.19.camel@palm>
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On Sun, 27 Mar 2005, Stephan Uphoff wrote: > On Tue, 2005-03-15 at 09:28, Stephan Uphoff wrote: > > On Tue, 2005-03-15 at 00:39, Jeff Roberson wrote: > > > On Mon, 14 Mar 2005, Stephan Uphoff wrote: > > > > > > > On Mon, 2005-03-14 at 21:38, Jeff Roberson wrote: > > > > > I have a patch at http://www.chesapeake.net/~jroberson/freevnodes.diff > > > > > that allows us to start reclaiming vnodes from the free list and release > > > > > their memory. It also changes the semantics of wantfreevnodes, and makes > > > > > getnewvnode() much prettier. > > > > > > > > > > The changes attempt to keep some number of vnodes, currently 2.5% of > > > > > desiredvnodes, that are free in memory. Free vnodes are vnodes which > > > > > have no references or pages in memory. For example, if an application > > > > > simply stat's a vnode, it will end up on the free list at the end of the > > > > > operation. The algorithm that is currently in place will immediately > > > > > recycle these vnodes once there is enough pressure, which will cause us to > > > > > do a full lookup and reread the inode, etc. as soon as it is stat'd again. > > > > > > > > > > This also removes the recycling from the getnewvnode() path. Instead, it > > > > > is done by a new helper function that is called from vnlru_proc(). This > > > > > function just frees vnodes from the head of the list until we reach our > > > > > wantfreevnodes target. > > > > > > > > > > I haven't perf tested this yet, but I have a box that is doing a > > > > > buildworld with a fairly constant freevnodes count which shows that vnodes > > > > > are actually being uma_zfree'd. > > > > > > > > > > Comments? Anyone willing to do some perf tests for me? > > > > > > > > > > Thanks, > > > > > Jeff > > > > > > > > Just looked at the raw diff and might have missed it - how are the > > > > parent directory "name" cache entries ( vnode fields v_dd, v_ddid) > > > > handled? > > > > > > Just as they were before, by calling cache_purge. > > > > This purges the fields of the vnode that will be recycled. > > > > I am worried about the v_dd,v_ddid fields of a directory B that has the > > to be released vnode A as parent. (Obviously in this case there is no > > namecache entry with the vnode A as the directory (nc_dvp)) > > > > Right now A is type stable - but if A is released, access to B->v_dd > > may cause a page fault. > > > > Stephan > > Jeff, > > Do you plan to address the problem now that the code is checked in? Vnodes with children in the name cache are held with vhold() and not recycled. > > Stephan >
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