many regions checked again and again despite knowing the pages
contained were not usable and only satisfied the alignment constraints
This case was compounded, especially for large allocations, by the
practice of looping from the top of memory so as to keep out of the
important low-memory regions. While the old contigmalloc(9) has the
same problem, it is not as noticeable due to looping from the low
memory to high.
This degenerate case is fixed, as well as reversing the sense of the
rest of the loops within it, to provide a tremendous speed increase.
This makes the best case O(n * VM overhead) much more likely than the
worst case O(4 * VM overhead). For comparison, the worst case for old
contigmalloc would be O(5 * VM overhead) in addition to its strategy
of turning used memory into free being highly pessimal.
Also, fix a bug that in practice most likely couldn't have been triggered,
int the new contigmalloc(9): it walked backwards from the end of memory
without accounting for how many pages it needed. Potentially, nonexistant
pages could have been mapped. This hasn't occurred because the kernel
generally requests as its first contigmalloc(9) a single page.
Reported by: Nicolas Dehaine <nicko@stbernard.com>, wes
MFC After: 1 month
More testing by: Nicolas Dehaine <nicko@stbernard.com>, wes
Historically, our contigmalloc1() and contigmalloc2() assumes
that a page in PQ_CACHE can be unconditionally reused by busying
and freeing it. Unfortunatelly, when object happens to be not
NULL, the code will set m->object to NULL and disregard the fact
that the page is actually in the VM page bucket, resulting in
page bucket hash table corruption and finally, a filesystem
corruption, or a 'page not in hash' panic.
This commit has borrowed the idea taken from DragonFlyBSD's fix
to the VM fix by Matthew Dillon[1]. This version of patch will
do the following checks:
- When scanning pages in PQ_CACHE, check hold_count and
skip over pages that are held temporarily.
- For pages in PQ_CACHE and selected as candidate of being
freed, check if it is busy at that time.
Note: It seems that this is might be unrelated to kern/72539.
Obtained from: DragonFlyBSD, sys/vm/vm_contig.c,v 1.11 and 1.12 [1]
Reminded by: Matt Dillon
Reworked by: alc
MFC After: 1 week
need for most calls to vm_page_busy(). Specifically, most calls to
vm_page_busy() occur immediately prior to a call to vm_page_remove().
In such cases, the containing vm object is locked across both calls.
Consequently, the setting of the vm page's PG_BUSY flag is not even
visible to other threads that are following the synchronization
protocol.
This change (1) eliminates the calls to vm_page_busy() that
immediately precede a call to vm_page_remove() or functions, such as
vm_page_free() and vm_page_rename(), that call it and (2) relaxes the
requirement in vm_page_remove() that the vm page's PG_BUSY flag is
set. Now, the vm page's PG_BUSY flag is set only when the vm object
lock is released while the vm page is still in transition. Typically,
this is when it is undergoing I/O.
vm_page_sleep_if_busy(). (The motivation being to transition
synchronization of the vm_page's PG_BUSY flag from the global page queues
lock to the per-object lock.)
improved chance of working despite pressure from running programs.
Instead of trying to throw a bunch of pages out to swap and hope for
the best, only a range that can potentially fulfill contigmalloc(9)'s
request will have its contents paged out (potentially, not forcibly)
at a time.
The new contigmalloc operation still operates in three passes, but it
could potentially be tuned to more or less. The first pass only looks
at pages in the cache and free pages, so they would be thrown out
without having to block. If this is not enough, the subsequent passes
page out any unwired memory. To combat memory pressure refragmenting
the section of memory being laundered, each page is removed from the
systems' free memory queue once it has been freed so that blocking
later doesn't cause the memory laundered so far to get reallocated.
The page-out operations are now blocking, as it would make little sense
to try to push out a page, then get its status immediately afterward
to remove it from the available free pages queue, if it's unlikely to
have been freed. Another change is that if KVA allocation fails, the
allocated memory segment will be freed and not leaked.
There is a sysctl/tunable, defaulting to on, which causes the old
contigmalloc() algorithm to be used. Nonetheless, I have been using
vm.old_contigmalloc=0 for over a month. It is safe to switch at
run-time to see the difference it makes.
A new interface has been used which does not require mapping the
allocated pages into KVA: vm_page.h functions vm_page_alloc_contig()
and vm_page_release_contig(). These are what vm.old_contigmalloc=0
uses internally, so the sysctl/tunable does not affect their operation.
When using the contigmalloc(9) and contigfree(9) interfaces, memory
is now tracked with malloc(9) stats. Several functions have been
exported from kern_malloc.c to allow other subsystems to use these
statistics, as well. This invalidates the BUGS section of the
contigmalloc(9) manpage.
1. Remove a race whereby contigmalloc() would deadlock against the
running processes in the system if they kept reinstantiating
the memory on the active and inactive page queues that it was
trying to flush out. The process doing the contigmalloc() would
sit in "swwrt" forever and the swap pager would be going at full
force, but never get anywhere. Instead of doing it until the
queues are empty, launder for as many iterations as there are
pages in the queue.
2. Do all laundering to swap synchronously; previously, the vnode
laundering was synchronous and the swap laundering not.
3. Increase the number of launder-or-allocate passes to three, from
two, while failing without bothering to do all the laundering on
the third pass if allocation was not possible. This effectively
gives exactly two chances to launder enough contiguous memory,
helpful with high memory churn where a lot of memory from one pass
to the next (and during a single laundering loop) becomes dirtied
again.
I can now reliably hot-plug hardware requiring a 256KB contigmalloc()
without having the kldload/cbb ithread sit around failing to make
progress, while running a busy X session. Previously, it took killing
X to get contigmalloc() to get further (that is, quiescing the system),
and even then contigmalloc() returned failure.
unnecessary and wrong. While it is necessary to verify that the page is
still free after dropping and reacquiring the free page queue lock, the
physical contiguity of the page can not change, making this check
unnecessary. This check was wrong in that it could cause an out-of-bounds
array access.
Tested by: rwatson
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.
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 and vm_page.c's revision 1.275.
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.
to the object's type field and the call to vm_pageout_flush() are
synchronized.
- The above change allows for the eliminaton of the last parameter
to vm_pageout_flush().
- Synchronize access to the page's valid field in vm_pageout_flush()
using the containing object's lock.
- All those diffs to syscalls.master for each architecture *are*
necessary. This needed clarification; the stub code generation for
mlockall() was disabled, which would prevent applications from
linking to this API (suggested by mux)
- Giant has been quoshed. It is no longer held by the code, as
the required locking has been pushed down within vm_map.c.
- Callers must specify VM_MAP_WIRE_HOLESOK or VM_MAP_WIRE_NOHOLES
to express their intention explicitly.
- Inspected at the vmstat, top and vm pager sysctl stats level.
Paging-in activity is occurring correctly, using a test harness.
- The RES size for a process may appear to be greater than its SIZE.
This is believed to be due to mappings of the same shared library
page being wired twice. Further exploration is needed.
- Believed to back out of allocations and locks correctly
(tested with WITNESS, MUTEX_PROFILING, INVARIANTS and DIAGNOSTIC).
PR: kern/43426, standards/54223
Reviewed by: jake, alc
Approved by: jake (mentor)
MFC after: 2 weeks
- Add a parameter to vm_pageout_flush() that tells vm_pageout_flush()
whether its caller has locked the vm_object. (This is a temporary
measure to bootstrap vm_object locking.)
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)
vm_map_user_pageable().
o Remove vm_map_pageable() and vm_map_user_pageable().
o Remove vm_map_clear_recursive() and vm_map_set_recursive(). (They were
only used by vm_map_pageable() and vm_map_user_pageable().)
Reviewed by: tegge
kernel map and object in a manner that contigfree() is actually able to
free. Previously contigfree() freed up the KVA space but could not
unwire & free the underlying VM pages due to mismatched pageability between
the map entry and the VM pages.
Submitted by: Thomas Moestl <tmoestl@gmx.net>
Testing by: mark tinguely <tinguely@web.cs.ndsu.nodak.edu>
MFC after: 3 days
Note ALL MODULES MUST BE RECOMPILED
make the kernel aware that there are smaller units of scheduling than the
process. (but only allow one thread per process at this time).
This is functionally equivalent to teh previousl -current except
that there is a thread associated with each process.
Sorry john! (your next MFC will be a doosie!)
Reviewed by: peter@freebsd.org, dillon@freebsd.org
X-MFC after: ha ha ha ha
Also removed some spl's and added some VM mutexes, but they are not actually
used yet, so this commit does not really make any operational changes
to the system.
vm_page.c relates to vm_page_t manipulation, including high level deactivation,
activation, etc... vm_pageq.c relates to finding free pages and aquiring
exclusive access to a page queue (exclusivity part not yet implemented).
And the world still builds... :-)
