Date: Tue, 25 Sep 2007 00:15:21 -0700 (PDT) From: Jeff Roberson <jroberson@chesapeake.net> To: Alan Cox <alc@FreeBSD.org> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/amd64/include vmparam.h src/sys/arm/include vmparam.h src/sys/i386/include vmparam.h src/sys/ia64/include vmparam.h src/sys/kern kern_exec.c vfs_bio.c src/sys/powerpc/include vmparam.h src/sys/sparc64/include ... Message-ID: <20070925001250.B547@10.0.0.1> In-Reply-To: <200709250625.l8P6P7w7082233@repoman.freebsd.org> References: <200709250625.l8P6P7w7082233@repoman.freebsd.org>
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On Tue, 25 Sep 2007, Alan Cox wrote: > alc 2007-09-25 06:25:07 UTC > > FreeBSD src repository > > Modified files: > sys/amd64/include vmparam.h > sys/arm/include vmparam.h > sys/i386/include vmparam.h > sys/ia64/include vmparam.h > sys/kern kern_exec.c vfs_bio.c > sys/powerpc/include vmparam.h > sys/sparc64/include vmparam.h > sys/sun4v/include vmparam.h > sys/sys vmmeter.h > sys/vm vm_contig.c vm_fault.c vm_map.c > vm_object.c vm_object.h vm_page.c > vm_page.h vm_pageout.c vm_pageq.c > vm_phys.c vm_phys.h > Log: > Change the management of cached pages (PQ_CACHE) in two fundamental > ways: Excellent work Alan! I'm glad this is making it in. Thanks, Jeff > > (1) Cached pages are no longer kept in the object's resident page > splay tree and memq. Instead, they are kept in a separate per-object > splay tree of cached pages. However, access to this new per-object > splay tree is synchronized by the _free_ page queues lock, not to be > confused with the heavily contended page queues lock. Consequently, a > cached page can be reclaimed by vm_page_alloc(9) without acquiring the > object's lock or the page queues lock. > > This solves a problem independently reported by tegge@ and Isilon. > Specifically, they observed the page daemon consuming a great deal of > CPU time because of pages bouncing back and forth between the cache > queue (PQ_CACHE) and the inactive queue (PQ_INACTIVE). The source of > this problem turned out to be a deadlock avoidance strategy employed > when selecting a cached page to reclaim in vm_page_select_cache(). > However, the root cause was really that reclaiming a cached page > required the acquisition of an object lock while the page queues lock > was already held. Thus, this change addresses the problem at its > root, by eliminating the need to acquire the object's lock. > > Moreover, keeping cached pages in the object's primary splay tree and > memq was, in effect, optimizing for the uncommon case. Cached pages > are reclaimed far, far more often than they are reactivated. Instead, > this change makes reclamation cheaper, especially in terms of > synchronization overhead, and reactivation more expensive, because > reactivated pages will have to be reentered into the object's primary > splay tree and memq. > > (2) Cached pages are now stored alongside free pages in the physical > memory allocator's buddy queues, increasing the likelihood that large > allocations of contiguous physical memory (i.e., superpages) will > succeed. > > Finally, as a result of this change long-standing restrictions on when > and where a cached page can be reclaimed and returned by > vm_page_alloc(9) are eliminated. Specifically, calls to > vm_page_alloc(9) specifying VM_ALLOC_INTERRUPT can now reclaim and > return a formerly cached page. Consequently, a call to malloc(9) > specifying M_NOWAIT is less likely to fail. > > Discussed with: many over the course of the summer, including jeff@, > Justin Husted @ Isilon, peter@, tegge@ > Tested by: an earlier version by kris@ > Approved by: re (kensmith) > > Revision Changes Path > 1.49 +3 -2 src/sys/amd64/include/vmparam.h > 1.11 +3 -2 src/sys/arm/include/vmparam.h > 1.45 +3 -2 src/sys/i386/include/vmparam.h > 1.17 +3 -2 src/sys/ia64/include/vmparam.h > 1.308 +1 -1 src/sys/kern/kern_exec.c > 1.527 +4 -10 src/sys/kern/vfs_bio.c > 1.10 +3 -2 src/sys/powerpc/include/vmparam.h > 1.18 +3 -2 src/sys/sparc64/include/vmparam.h > 1.5 +3 -2 src/sys/sun4v/include/vmparam.h > 1.34 +2 -2 src/sys/sys/vmmeter.h > 1.63 +2 -11 src/sys/vm/vm_contig.c > 1.236 +8 -21 src/sys/vm/vm_fault.c > 1.388 +7 -11 src/sys/vm/vm_map.c > 1.383 +30 -14 src/sys/vm/vm_object.c > 1.114 +1 -0 src/sys/vm/vm_object.h > 1.354 +271 -86 src/sys/vm/vm_page.c > 1.151 +11 -15 src/sys/vm/vm_page.h > 1.292 +2 -35 src/sys/vm/vm_pageout.c > 1.35 +0 -27 src/sys/vm/vm_pageq.c > 1.4 +115 -33 src/sys/vm/vm_phys.c > 1.3 +3 -0 src/sys/vm/vm_phys.h >
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