additional information, when the page is guaranteed to not belong to a
paging queue. Usually, this results in a lot of type casts which make
reasoning about the code correctness harder.
Sometimes m->object is used instead of pageq, which could cause real
and confusing bugs if non-NULL m->object is leaked. See r141955 and
r253140 for examples.
Change the pageq member into a union containing explicitly-typed
members. Use them instead of type-punning or abusing m->object in x86
pmaps, uma and vm_page_alloc_contig().
Requested and reviewed by: alc
Sponsored by: The FreeBSD Foundation
Unify the 2 concept into a real, minimal, sxlock where the shared
acquisition represent the soft busy and the exclusive acquisition
represent the hard busy.
The old VPO_WANTED mechanism becames the hard-path for this new lock
and it becomes per-page rather than per-object.
The vm_object lock becames an interlock for this functionality:
it can be held in both read or write mode.
However, if the vm_object lock is held in read mode while acquiring
or releasing the busy state, the thread owner cannot make any
assumption on the busy state unless it is also busying it.
Also:
- Add a new flag to directly shared busy pages while vm_page_alloc
and vm_page_grab are being executed. This will be very helpful
once these functions happen under a read object lock.
- Move the swapping sleep into its own per-object flag
The KPI is heavilly changed this is why the version is bumped.
It is very likely that some VM ports users will need to change
their own code.
Sponsored by: EMC / Isilon storage division
Discussed with: alc
Reviewed by: jeff, kib
Tested by: gavin, bapt (older version)
Tested by: pho, scottl
into threads each processing queue in a single domain. The structure
of the pagedaemons and queues is kept intact, most of the changes come
from the need for code to find an owning page queue for given page,
calculated from the segment containing the page.
The tie between NUMA domain and pagedaemon thread/pagequeue split is
rather arbitrary, the multithreaded daemon could be allowed for the
single-domain machines, or one domain might be split into several page
domains, to further increase concurrency.
Right now, each pagedaemon thread tries to reach the global target,
precalculated at the start of the pass. This is not optimal, since it
could cause excessive page deactivation and freeing. The code should
be changed to re-check the global page deficit state in the loop after
some number of iterations.
The pagedaemons reach the quorum before starting the OOM, since one
thread inability to meet the target is normal for split queues. Only
when all pagedaemons fail to produce enough reusable pages, OOM is
started by single selected thread.
Launder is modified to take into account the segments layout with
regard to the region for which cleaning is performed.
Based on the preliminary patch by jeff, sponsored by EMC / Isilon
Storage Division.
Reviewed by: alc
Tested by: pho
Sponsored by: The FreeBSD Foundation
- Don't short-circuit aging tests for unmapped objects. This biases
against unmapped file pages and transient mappings.
- Always honor PGA_REFERENCED. We can now use this after soft busying
to lazily restart the LRU.
- Don't transition directly from active to cached bypassing the inactive
queue. This frees recently used data much too early.
- Rename actcount to act_delta to be more consistent with use and meaning.
Reviewed by: kib, alc
Sponsored by: EMC / Isilon Storage Division
per-page lock rather than vm_object lock, without any further overhead.
Make the formal switch.
Sponsored by: EMC / Isilon storage division
Reviewed by: alc
Tested by: pho
future further optimizations where the vm_object lock will be held
in read mode most of the time the page cache resident pool of pages
are accessed for reading purposes.
The change is mostly mechanical but few notes are reported:
* The KPI changes as follow:
- VM_OBJECT_LOCK() -> VM_OBJECT_WLOCK()
- VM_OBJECT_TRYLOCK() -> VM_OBJECT_TRYWLOCK()
- VM_OBJECT_UNLOCK() -> VM_OBJECT_WUNLOCK()
- VM_OBJECT_LOCK_ASSERT(MA_OWNED) -> VM_OBJECT_ASSERT_WLOCKED()
(in order to avoid visibility of implementation details)
- The read-mode operations are added:
VM_OBJECT_RLOCK(), VM_OBJECT_TRYRLOCK(), VM_OBJECT_RUNLOCK(),
VM_OBJECT_ASSERT_RLOCKED(), VM_OBJECT_ASSERT_LOCKED()
* The vm/vm_pager.h namespace pollution avoidance (forcing requiring
sys/mutex.h in consumers directly to cater its inlining functions
using VM_OBJECT_LOCK()) imposes that all the vm/vm_pager.h
consumers now must include also sys/rwlock.h.
* zfs requires a quite convoluted fix to include FreeBSD rwlocks into
the compat layer because the name clash between FreeBSD and solaris
versions must be avoided.
At this purpose zfs redefines the vm_object locking functions
directly, isolating the FreeBSD components in specific compat stubs.
The KPI results heavilly broken by this commit. Thirdy part ports must
be updated accordingly (I can think off-hand of VirtualBox, for example).
Sponsored by: EMC / Isilon storage division
Reviewed by: jeff
Reviewed by: pjd (ZFS specific review)
Discussed with: alc
Tested by: pho
similar changes had to be made in various places throughout the machine-
independent virtual memory layer to support the new vm object type.
However, in most of these places, it's actually not the type of the vm
object that matters to us but instead certain attributes of its pages.
For example, OBJT_DEVICE, OBJT_MGTDEVICE, and OBJT_SG objects contain
fictitious pages. In other words, in most of these places, we were
testing the vm object's type to determine if it contained fictitious (or
unmanaged) pages.
To both simplify the code in these places and make the addition of future
vm object types easier, this change introduces two new vm object flags
that describe attributes of the vm object's pages, specifically, whether
they are fictitious or unmanaged.
Reviewed and tested by: kib
the call to pmap_remove_all() within vm_page_cache() is usually redundant.
This change eliminates that call to pmap_remove_all() and introduces a
call to pmap_remove_all() before vm_page_cache() in the one place where
it didn't already exist.
When iterating over a paging queue, if the object containing the current
page has a zero reference count, then the page can't have any managed
mappings. So, a call to pmap_remove_all() is pointless.
Change a panic() call in vm_page_cache() to a KASSERT().
MFC after: 6 weeks
In particular, do not lock Giant conditionally when calling into the
filesystem module, remove the VFS_LOCK_GIANT() and related
macros. Stop handling buffers belonging to non-mpsafe filesystems.
The VFS_VERSION is bumped to indicate the interface change which does
not result in the interface signatures changes.
Conducted and reviewed by: attilio
Tested by: pho
vm_page_sleep(). vm_page_sleep() is no longer called with this lock
held.
Eliminate assertions that the page queues lock is NOT held. These
assertions won't translate well to having distinct locks on the active
and inactive page queues, and they really aren't that useful.
MFC after: 3 weeks
queues lock is acquired before the page lock is released, there is no
guarantee that the page will still be in that same page queue when
vm_page_requeue() is called.
Reported by: pho
In collaboration with: kib
MFC after: 3 days
ago, sleeping on busy pages in vm_pageout_launder() made sense. The call
to vm_pageout_flush() specified asynchronous I/O and sleeping on busy pages
blocked vm_pageout_launder() until the flush had completed. However, in
CVS revision 1.35 of vm/vm_contig.c, the call to vm_pageout_flush() was
changed to request synchronous I/O, but the sleep on busy pages was not
removed.
them alone.
Process the act_count updates for the held pages in the vm_pageout
loop over the inactive queue, instead of refusing to do anything with
such page.
Clarify the intent of the addl_page_shortage counter and change its
use for pages which are not processed in the loop according to the
description.
Reviewed by: alc
MFC after: 2 weeks
inactive queue, unless busy page is found.
Dropping the mutex often should allow the other lock acquires to
proceed without waiting for whole inactive scan to finish. On machines
with lot of physical memory scan often need to iterate a lot before it
finishes or finds a page which requires laundring, causing high
latency for other lock waiters.
Suggested and reviewed by: alc
MFC after: 3 weeks
layer, but it is read directly by the MI VM layer. This change introduces
pmap_page_is_write_mapped() in order to completely encapsulate all direct
access to PGA_WRITEABLE in the pmap layer.
Aesthetics aside, I am making this change because amd64 will likely begin
using an alternative method to track write mappings, and having
pmap_page_is_write_mapped() in place allows me to make such a change
without further modification to the MI VM layer.
As an added bonus, tidy up some nearby comments concerning page flags.
Reviewed by: kib
MFC after: 6 weeks
if the filesystem performed short write and we are skipping the page
due to this.
Propogate write error from the pager back to the callers of
vm_pageout_flush(). Report the failure to write a page from the
requested range as the FALSE return value from vm_object_page_clean(),
and propagate it back to msync(2) to return EIO to usermode.
While there, convert the clearobjflags variable in the
vm_object_page_clean() and arguments of the helper functions to
boolean.
PR: kern/165927
Reviewed by: alc
MFC after: 2 weeks
flags field. Updates to the atomic flags are performed using the atomic
ops on the containing word, do not require any vm lock to be held, and
are non-blocking. The vm_page_aflag_set(9) and vm_page_aflag_clear(9)
functions are provided to modify afalgs.
Document the changes to flags field to only require the page lock.
Introduce vm_page_reference(9) function to provide a stable KPI and
KBI for filesystems like tmpfs and zfs which need to mark a page as
referenced.
Reviewed by: alc, attilio
Tested by: marius, flo (sparc64); andreast (powerpc, powerpc64)
Approved by: re (bz)
won't happen before 9.0. This commit adds "#ifdef RACCT" around all the
"PROC_LOCK(p); racct_whatever(p, ...); PROC_UNLOCK(p)" instances, in order
to avoid useless locking/unlocking in kernels built without "options RACCT".
- Hold the proc lock while changing the state from PRS_NEW to PRS_NORMAL
in fork to honor the locking requirements. While here, expand the scope
of the PROC_LOCK() on the new process (p2) to avoid some LORs. Previously
the code was locking the new child process (p2) after it had locked the
parent process (p1). However, when locking two processes, the safe order
is to lock the child first, then the parent.
- Fix various places that were checking p_state against PRS_NEW without
having the process locked to use PROC_LOCK(). Every place was already
locking the process, just after the PRS_NEW check.
- Remove or reduce the use of PROC_SLOCK() for places that were checking
p_state against PRS_NEW. The PROC_LOCK() alone is sufficient for reading
the current state.
- Reorder fill_kinfo_proc() slightly so it only acquires PROC_SLOCK() once.
MFC after: 1 week
which are not yet fully initialized (i.e. ones with p_state == PRS_NEW).
Without it, we could panic in _thread_lock_flags().
Note that there may be other instances of FOREACH_PROC_IN_SYSTEM() that
require similar fix.
Reported by: pho, keramida
Discussed with: kib
hold this lock until the end of the function.
With the aforementioned change to vm_pageout_clean(), page locks don't need
to support recursive (MTX_RECURSE) or duplicate (MTX_DUPOK) acquisitions.
Reviewed by: kib
backing storage. Such pages might be then reused, racing with the
assert in vm_object_page_collect_flush() that verified that dirty
pages from the run (most likely, pages with VM_PAGER_AGAIN status) are
write-protected still. In fact, the page indexes for the pages that
were removed from the object page list should be ignored by
vm_object_page_clean().
Return the length of successfully written run from vm_pageout_flush(),
that is, the count of pages between requested page and first page
after requested with status VM_PAGER_AGAIN. Supply the requested page
index in the array to vm_pageout_flush(). Use the returned run length
to forward the index of next page to clean in vm_object_page_clean().
Reported by: avg
Reviewed by: alc
MFC after: 1 week
in a range must be checked when calling pmap_remove(). Calling
pmap_remove() from vm_pageout_map_deactivate_pages() with the entire range
of the map could result in attempting to demap an extraordinary number
of pages (> 10^15), so iterate through each map entry and unmap each of
them individually.
MFC after: 6 weeks
Previously, the caller unlocked the page, and vm_pageout_clean()
immediately reacquired the page lock. Also, assert rather than test
that the page is neither busy nor held. Since vm_pageout_clean() is
called with the object and page locked, the page can't have changed
state since the caller verified that the page is neither busy nor
held.
vm_pageout_clean(). When iterating over a range of pages, these functions
can be cheaper than vm_page_lookup() because their implementation takes
advantage of the vm_object's memq being ordered.
Reviewed by: kib@
MFC after: 3 weeks
and vm_pageout_page_stats(). These checks were recently introduced by
the first page locking commit, r207410, but they are not needed. At
the same time, eliminate some redundant accesses to the page's object
field. (These accesses should have neen eliminated by r207410.)
Make the assertion in vm_page_flag_set() stricter. Specifically, only
managed pages should have PG_WRITEABLE set.
Add a comment documenting an assertion to vm_page_flag_clear().
It has long been the case that fictitious pages have their wire count
permanently set to one. Add comments to vm_page_wire() and
vm_page_unwire() documenting this. Add assertions to these functions
as well.
Update the comment describing vm_page_unwire(). Much of the old
comment had little to do with vm_page_unwire(), but a lot to do with
_vm_page_deactivate(). Move relevant parts of the old comment to
_vm_page_deactivate().
Only pages that belong to an object can be paged out. Therefore, it
is pointless for vm_page_unwire() to acquire the page queues lock and
enqueue such pages in one of the paging queues. Generally speaking,
such pages are immediately freed after the call to vm_page_unwire().
Previously, it was the call to vm_page_free() that reacquired the page
queues lock and removed these pages from the paging queues. Now, we
will never acquire the page queues lock for this case. (It is also
worth noting that since both vm_page_unwire() and vm_page_free()
occurred with the page locked, the page daemon never saw the page with
its object field set to NULL.)
Change the panic with vm_page_unwire() to provide a more precise message.
Reviewed by: kib@
PG_REFERENCED changes in vm_pageout_object_deactivate_pages().
Simplify this function's inner loop using TAILQ_FOREACH(), and shorten
some of its overly long lines. Update a stale comment.
Assert that PG_REFERENCED may be cleared only if the object containing
the page is locked. Add a comment documenting this.
Assert that a caller to vm_page_requeue() holds the page queues lock,
and assert that the page is on a page queue.
Push down the page queues lock into pmap_ts_referenced() and
pmap_page_exists_quick(). (As of now, there are no longer any pmap
functions that expect to be called with the page queues lock held.)
Neither pmap_ts_referenced() nor pmap_page_exists_quick() should ever
be passed an unmanaged page. Assert this rather than returning "0"
and "FALSE" respectively.
ARM:
Simplify pmap_page_exists_quick() by switching to TAILQ_FOREACH().
Push down the page queues lock inside of pmap_clearbit(), simplifying
pmap_clear_modify(), pmap_clear_reference(), and pmap_remove_write().
Additionally, this allows for avoiding the acquisition of the page
queues lock in some cases.
PowerPC/AIM:
moea*_page_exits_quick() and moea*_page_wired_mappings() will never be
called before pmap initialization is complete. Therefore, the check
for moea_initialized can be eliminated.
Push down the page queues lock inside of moea*_clear_bit(),
simplifying moea*_clear_modify() and moea*_clear_reference().
The last parameter to moea*_clear_bit() is never used. Eliminate it.
PowerPC/BookE:
Simplify mmu_booke_page_exists_quick()'s control flow.
Reviewed by: kib@
independent code. Move this code into mincore(), and eliminate the
page queues lock from pmap_mincore().
Push down the page queues lock into pmap_clear_modify(),
pmap_clear_reference(), and pmap_is_modified(). Assert that these
functions are never passed an unmanaged page.
Eliminate an inaccurate comment from powerpc/powerpc/mmu_if.m:
Contrary to what the comment says, pmap_mincore() is not simply an
optimization. Without a complete pmap_mincore() implementation,
mincore() cannot return either MINCORE_MODIFIED or MINCORE_REFERENCED
because only the pmap can provide this information.
Eliminate the page queues lock from vfs_setdirty_locked_object(),
vm_pageout_clean(), vm_object_page_collect_flush(), and
vm_object_page_clean(). Generally speaking, these are all accesses
to the page's dirty field, which are synchronized by the containing
vm object's lock.
Reduce the scope of the page queues lock in vm_object_madvise() and
vm_page_dontneed().
Reviewed by: kib (an earlier version)
vm_page_try_to_free(). Consequently, push down the page queues lock into
pmap_enter_quick(), pmap_page_wired_mapped(), pmap_remove_all(), and
pmap_remove_write().
Push down the page queues lock into Xen's pmap_page_is_mapped(). (I
overlooked the Xen pmap in r207702.)
Switch to a per-processor counter for the total number of pages cached.
