path: root/sys/sys/vmmeter.h
diff options
authorAlan Cox <alc@FreeBSD.org>2007-09-25 06:25:06 +0000
committerAlan Cox <alc@FreeBSD.org>2007-09-25 06:25:06 +0000
commit7bfda801a8efe3352862aa54dd5d22cd3c005ac3 (patch)
treed6ef2df64ec2f1114828f2caa046592acbdfad76 /sys/sys/vmmeter.h
parent977b6507cb88cf79c02bd13f446e6b96dde499aa (diff)
Change the management of cached pages (PQ_CACHE) in two fundamental
ways: (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)
Notes: svn path=/head/; revision=172317
Diffstat (limited to 'sys/sys/vmmeter.h')
1 files changed, 2 insertions, 2 deletions
diff --git a/sys/sys/vmmeter.h b/sys/sys/vmmeter.h
index bdd196464357..2b4794a44a8e 100644
--- a/sys/sys/vmmeter.h
+++ b/sys/sys/vmmeter.h
@@ -68,7 +68,7 @@ struct vmmeter {
u_int v_vnodepgsin; /* (p) vnode_pager pages paged in */
u_int v_vnodepgsout; /* (p) vnode pager pages paged out */
u_int v_intrans; /* (p) intransit blocking page faults */
- u_int v_reactivated; /* (q) pages reactivated from free list */
+ u_int v_reactivated; /* (f) pages reactivated from free list */
u_int v_pdwakeups; /* (f) times daemon has awaken from sleep */
u_int v_pdpages; /* (q) pages analyzed by daemon */
@@ -89,7 +89,7 @@ struct vmmeter {
u_int v_active_count; /* (q) pages active */
u_int v_inactive_target; /* (c) pages desired inactive */
u_int v_inactive_count; /* (q) pages inactive */
- u_int v_cache_count; /* (q) pages on buffer cache queue */
+ u_int v_cache_count; /* (f) pages on buffer cache queue */
u_int v_cache_min; /* (c) min pages desired on cache queue */
u_int v_cache_max; /* (c) max pages in cached obj */
u_int v_pageout_free_min; /* (c) min pages reserved for kernel */