Some of the conditions that caused vm_page_select_cache() to deactivate a
page were wrong. For example, deactivating an unmanaged or wired page is a
nop. Thus, if vm_page_select_cache() had ever encountered an unmanaged or
wired page, it would have looped forever. Now, we assert that the page is
neither unmanaged nor wired.
caller to vm_page_grab(). Although this gives VM_ALLOC_ZERO a
different meaning for vm_page_grab() than for vm_page_alloc(), I feel
such change is necessary to accomplish other goals. Specifically, I
want to make the PG_ZERO flag immutable between the time it is
allocated by vm_page_alloc() and freed by vm_page_free() or
vm_page_free_zero() to avoid locking overheads. Once we gave up on
the ability to automatically recognize a zeroed page upon entry to
vm_page_free(), the ability to mutate the PG_ZERO flag became useless.
Instead, I would like to say that "Once a page becomes valid, its
PG_ZERO flag must be ignored."
vm_page_free() is called. The problem with holding this lock is that it is
a spin lock and vm_page_free() may attempt the acquisition of a different
default-type lock.
could result in a panic "vm_page_cache: caching a dirty page, ...":
Access to the page must be restricted or removed before calling
vm_page_cache(). This race condition is identical in nature to that
which was addressed by vm_pageout.c's revision 1.251.
- Simplify the code surrounding the fix to this same race condition
in vm_pageout.c's revision 1.251. There should be no behavioral
change. Reviewed by: tegge
MFC after: 7 days
free pages queue. This is presently needed by contigmalloc1().
- Move a sanity check against attempted double allocation of two pages
to the same vm object offset from vm_page_alloc() to vm_page_insert().
This provides better protection because double allocation could occur
through a direct call to vm_page_insert(), such as that by
vm_page_rename().
- Modify contigmalloc1() to hold the mutex synchronizing access to the
free pages queue while it scans vm_page_array in search of free pages.
- Correct a potential leak of pages by contigmalloc1() that I introduced
in revision 1.20: We must convert all cache queue pages to free pages
before we begin removing free pages from the free queue. Otherwise,
if we have to restart the scan because we are unable to acquire the
vm object lock that is necessary to convert a cache queue page to a
free page, we leak those free pages already removed from the free queue.
vm object hasn't changed, the desired page will be at or near the root
of the vm object's splay tree, making vm_page_lookup() cheap. (The only
lock required for vm_page_lookup() is already held.) If, however, the
vm object has changed and retry was requested, eliminating the generation
check also eliminates a pointless acquisition and release of the page
queues lock.
This guard page would have trapped the problems with the MFC of the PAE
support to RELENG_4 at an earlier point in the sequence of events.
Submitted by: tegge
vm_pageout_scan(). Rationale: I don't like leaving a busy page in the
cache queue with neither the vm object nor the vm page queues lock held.
- Assert that the page is active in vm_pageout_page_stats().
pmap_copy_page() et al. to accept a vm_page_t rather than a physical
address. Also, this change will facilitate locking access to the vm page's
valid field.
color in vm_page_alloc(). (This also has small performance benefits.)
- Eliminate vm_page_select_free(); vm_page_alloc() might as well
call vm_pageq_find() directly.
releasing the lock only if we are about to sleep (e.g., vm_pager_get_pages()
or vm_pager_has_pages()). If we sleep, we have marked the vm object with
the paging-in-progress flag.
- Remove the Giant required from vm_page_free_toq(). (Any locking
errors will be caught by vm_page_remove().)
This remedies a panic that occurred when kmem_malloc(NOWAIT) performed
without Giant failed to allocate the necessary pages.
Reported by: phk
called without Giant; and obj_alloc() in turn calls vm_page_alloc()
without Giant. This causes an assertion failure in vm_page_alloc().
Fortunately, obj_alloc() is now MPSAFE. So, we need only clean up
some assertions.
- Weaken the assertion in vm_page_lookup() to require Giant only
if the vm_object isn't locked.
- Remove an assertion from vm_page_alloc() that duplicates a check
performed in vm_page_lookup().
In collaboration with: gallatin, jake, jeff
where physical addresses larger than virtual addresses, such as i386s
with PAE.
- Use this to represent physical addresses in the MI vm system and in the
i386 pmap code. This also changes the paddr parameter to d_mmap_t.
- Fix printf formats to handle physical addresses >4G in the i386 memory
detection code, and due to kvtop returning vm_paddr_t instead of u_long.
Note that this is a name change only; vm_paddr_t is still the same as
vm_offset_t on all currently supported platforms.
Sponsored by: DARPA, Network Associates Laboratories
Discussed with: re, phk (cdevsw change)
The objective being to eliminate some cases of page queues locking.
(See, for example, vm/vm_fault.c revision 1.160.)
Reviewed by: tegge
(Also, pointed out by tegge that I changed vm_fault.c before changing
vm_page.c. Oops.)
requests when the number of free pages is below the reserved threshold.
Previously, VM_ALLOC_ZERO was only honored when the number of free pages
was above the reserved threshold. Honoring it in all cases generally
makes sense, does no harm, and simplifies the code.
