Commit Graph

14 Commits

Author SHA1 Message Date
Alan Cox
beb3c3a9c5 Retire VM_PROT_READ_IS_EXEC. It was intended to be a micro-optimization,
but I see no benefit from it today.

VM_PROT_READ_IS_EXEC was only intended for use on processors that do not
distinguish between read and execute permission.  On an mmap(2) or
mprotect(2), it automatically added execute permission if the caller
specified permissions included read permission.  The hope was that this
would reduce the number of vm map entries needed to implement an address
space because there would be fewer neighboring vm map entries that differed
only in the presence or absence of VM_PROT_EXECUTE.  (See vm/vm_mmap.c
revision 1.56.)

Today, I don't see any real applications that benefit from
VM_PROT_READ_IS_EXEC.  In any case, vm map entries are now organized
as a self-adjusting binary search tree instead of an ordered list.  So,
the need for coalescing vm map entries is not as great as it once was.
2009-04-04 23:12:14 +00:00
Olivier Houchard
7202abb694 Add a comment explaining what ARM_KERN_DIRECTMAP is all about.
Suggested by:	raj
2009-01-22 15:36:11 +00:00
Alan Cox
b8e7fc24fe Add configuration knobs for the superpage reservation system. Initially,
the reservation will only be enabled on amd64.
2007-12-27 16:45:39 +00:00
Alan Cox
7bfda801a8 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)
2007-09-25 06:25:06 +00:00
Alan Cox
9211deca08 Add the machine-specific definitions for configuring the new physical
memory allocator.

Approved by:	re
2007-06-04 08:02:22 +00:00
Alan Cox
66ab556097 Eliminate some unused definitions that came from NetBSD. 2007-05-28 21:04:22 +00:00
Alan Cox
04a18977c8 Define every architecture as either VM_PHYSSEG_DENSE or
VM_PHYSSEG_SPARSE depending on whether the physical address space is
densely or sparsely populated with memory.  The effect of this
definition is to determine which of two implementations of
vm_page_array and PHYS_TO_VM_PAGE() is used.  The legacy
implementation is obtained by defining VM_PHYSSEG_DENSE, and a new
implementation that trades off time for space is obtained by defining
VM_PHYSSEG_SPARSE.  For now, all architectures except for ia64 and
sparc64 define VM_PHYSSEG_DENSE.  Defining VM_PHYSSEG_SPARSE on ia64
allows the entirety of my Itanium 2's memory to be used.  Previously,
only the first 1 GB could be used.  Defining VM_PHYSSEG_SPARSE on
sparc64 allows USIIIi-based systems to boot without crashing.

This change is a combination of Nathan Whitehorn's patch and my own
work in perforce.

Discussed with: kmacy, marius, Nathan Whitehorn
PR:		112194
2007-05-05 19:50:28 +00:00
Alan Cox
b554f899bd Eliminate unused definitions. (They came from NetBSD.)
Discussed with: cognet, grehan, marcel
2006-08-25 23:51:11 +00:00
Olivier Houchard
49953e11d7 Rewrite ARM_USE_SMALL_ALLOC so that instead of the current behavior, it maps
whole the physical memory, cached, using 1MB section mappings. This reduces
the address space available for user processes a bit, but given the amount of
memory a typical arm machine has, it is not (yet) a big issue.
It then provides a uma_small_alloc() that works as it does for architectures
which have a direct mapping.
2006-08-08 20:59:38 +00:00
Olivier Houchard
56e472e2b5 Add a new arm-specific option, ARM_USE_SMALL_ALLOC. If defined, it provides
an implementation of uma_small_alloc() which tries to preallocate memory
1MB per 1MB, and maps it into a section mapping.
2005-06-07 23:04:24 +00:00
Warner Losh
d8315c79d9 Start all license statements with /*- 2005-01-05 21:58:49 +00:00
Olivier Houchard
9f0f6bf453 Define VM_PROT_READ_IS_EXEC. 2004-09-23 22:29:43 +00:00
Olivier Houchard
5b17d1f95a Fix comments.
Spotted out by:	mux
2004-08-02 12:23:53 +00:00
Olivier Houchard
6fc729af63 Import FreeBSD/arm kernel bits.
It only supports sa1110 (on simics) right now, but xscale support should come
soon.
Some of the initial work has been provided by :
Stephane Potvin <sepotvin at videotron.ca>
Most of this comes from NetBSD.
2004-05-14 11:46:45 +00:00