Such pages are dequeued as they're encountered during the inactive queue
scan, so by the time we get to the active queue scan, they should have
already been subtracted from the inactive queue length.
Reviewed by: alc
Differential Revision: https://reviews.freebsd.org/D15479
vm_page_queue(), added in r333256, generalizes vm_pageout_page_queued(),
so use it instead. No functional change intended.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D15402
With r332974, when performing a synchronized access of a page's "queue"
field, one must first check whether the page is logically dequeued. If
so, then the page lock does not prevent the page from being removed
from its page queue. Intoduce vm_page_queue(), which returns the page's
logical queue index. In some cases, direct access to the "queue" field
is still required, but such accesses should be confined to sys/vm.
Reported and tested by: pho
Reviewed by: kib
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D15280
Currently both the page lock and a page queue lock must be held in
order to enqueue, dequeue or requeue a page in a given page queue.
The queue locks are a scalability bottleneck in many workloads. This
change reduces page queue lock contention by batching queue operations.
To detangle the page and page queue locks, per-CPU batch queues are
used to reference pages with pending queue operations. The requested
operation is encoded in the page's aflags field with the page lock
held, after which the page is enqueued for a deferred batch operation.
Page queue scans are similarly optimized to minimize the amount of
work performed with a page queue lock held.
Reviewed by: kib, jeff (previous versions)
Tested by: pho
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D14893
They were previously initialized by the corresponding page daemon
threads, but for vmd_inacthead this may be too late if
vm_page_deactivate_noreuse() is called during boot.
Reported and tested by: cperciva
Reviewed by: alc, kib
MFC after: 1 week
The division added in r331732 meant that we wouldn't attempt a
background laundering until at least v_free_target - v_free_min clean
pages had been freed by the page daemon since the last laundering. If
the inactive queue is depleted but not completely empty (e.g., because
it contains busy pages), it can thus take a long time to meet this
threshold. Restore the pre-r331732 behaviour of using a non-zero
background laundering threshold if at least one inactive queue scan has
elapsed since the last attempt at background laundering.
Submitted by: tijl (original version)
Rather than using the number of inactive queue scans as a metric for
how many clean pages are being freed by the page daemon, have the
page daemon keep a running counter of the number of pages it has freed,
and have the laundry thread use that when computing the background
laundering threshold.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D14884
vmd_free_count manipulation. Reduce the scope of the free lock by
using a pageout lock to synchronize sleep and wakeup. Only trigger
the pageout daemon on transitions between states. Drive all wakeup
operations directly as side-effects from freeing memory rather than
requiring an additional function call.
Reviewed by: markj, kib
Tested by: pho
Sponsored by: Netflix, Dell/EMC Isilon
Differential Revision: https://reviews.freebsd.org/D14612
Page daemon threads for other domains show up in ps(1) output as
"pagedaemon/domN", so let that be the case for domain 0 as well.
Submitted by: Kevin Bowling <kevin.bowling@kev009.com>
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D14518
With r329882, in the absence of a free page shortage we would only take
len(PQ_INACTIVE)+len(PQ_LAUNDRY) into account when deciding whether to
aggressively scan PQ_ACTIVE. Previously we would also include the
number of free pages in this computation, ensuring that we wouldn't scan
PQ_ACTIVE with plenty of free memory available. The change in behaviour
was most noticeable immediately after booting, when PQ_INACTIVE and
PQ_LAUNDRY are nearly empty.
Reviewed by: jeff
use it to regulate page daemon output.
This provides much smoother and more responsive page daemon output, anticipating
demand and avoiding pageout stalls by increasing the number of pages to match
the workload. This is a reimplementation of work done by myself and mlaier at
Isilon.
Reviewed by: bsdimp
Tested by: pho
Sponsored by: Netflix, Dell/EMC Isilon
Differential Revision: https://reviews.freebsd.org/D14402
Make vm_wait() take the vm_object argument which specifies the domain
set to wait for the min condition pass. If there is no object
associated with the wait, use curthread' policy domainset. The
mechanics of the wait in vm_wait() and vm_wait_domain() is supplied by
the new helper vm_wait_doms(), which directly takes the bitmask of the
domains to wait for passing min condition.
Eliminate pagedaemon_wait(). vm_domain_clear() handles the same
operations.
Eliminate VM_WAIT and VM_WAITPFAULT macros, the direct functions calls
are enough.
Eliminate several control state variables from vm_domain, unneeded
after the vm_wait() conversion.
Scetched and reviewed by: jeff
Tested by: pho
Sponsored by: The FreeBSD Foundation, Mellanox Technologies
Differential revision: https://reviews.freebsd.org/D14384
Previously, wiring a page would cause it to be removed from its page
queue. In the common case, unwiring causes it to be enqueued at the tail
of that page queue. This change modifies vm_page_wire() to not dequeue
the page, thus avoiding the highly contended page queue locks. Instead,
vm_page_unwire() takes care of requeuing the page as a single operation,
and the page daemon dequeues wired pages as they are encountered during
a queue scan to avoid needlessly revisiting them later. For pages in
PQ_ACTIVE we do even better, since a requeue is unnecessary.
The change improves scalability for some common workloads. For instance,
threads wiring pages into the buffer cache no longer need to modify
global page queues, and unwiring is usually done by the bufspace thread,
so concurrency is not as much of an issue. As another example, many
sysctl handlers wire the output buffer to avoid faults on copyout, and
since the buffer is likely to be in PQ_ACTIVE, we now entirely avoid
modifying the page queue in this case.
The change also adds a block comment describing some properties of
struct vm_page's reference counters, and the busy lock.
Reviewed by: jeff
Discussed with: alc, kib
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D11943
global to per-domain state. Protect reservations with the free lock
from the domain that they belong to. Refactor to make vm domains more
of a first class object.
Reviewed by: markj, kib, gallatin
Tested by: pho
Sponsored by: Netflix, Dell/EMC Isilon
Differential Revision: https://reviews.freebsd.org/D14000
Otherwise the page daemon will not reclaim pages and thus will not
wake threads sleeping in VM_WAIT.
Reported and tested by: pho
Reviewed by: alc, kib
X-MFC with: r327168
Differential Revision: https://reviews.freebsd.org/D13640
Both issues caused the page daemon to erroneously go to sleep when
applications are consuming free pages at a high rate, leaving the
application threads blocked in VM_WAIT.
1) After completing an inactive queue scan, concurrent allocations may
have prevented the page daemon from meeting the v_free_min threshold.
In this case, the page daemon was going to sleep even when the
inactive queue contained plenty of clean pages.
2) pagedaemon_wakeup() may be called without the free queues lock held.
This can lead to a lost wakeup if a call occurs after the page daemon
clears vm_pageout_wanted but before going to sleep.
Fix 1) by ensuring that we start a new inactive queue scan immediately
if v_free_count < v_free_min after a prior scan.
Fix 2) by adding a new subroutine, pagedaemon_wait(), called from
vm_wait() and vm_waitpfault(). It wakes up the page daemon if either
vm_pages_needed or vm_pageout_wanted is false, and atomically sleeps
on v_free_count.
Reported by: jeff
Reviewed by: alc
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D13424
The laundry thread keeps track of the number of inactive queue scans
performed by the page daemon, and was previously using the v_pdwakeups
counter to count them. However, in some cases the inactive queue may
be scanned multiple times after a single wakeup, so it's more accurate
to use a dedicated counter.
Reviewed by: alc, kib (previous version)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D13422
r292392 modified the active queue scan to weigh clean pages differently
from dirty pages when attempting to meet the inactive queue target. When
r306706 was merged into the PQ_LAUNDRY branch, this mechanism was
broken. Fix it by scalaing the correct page shortage variable.
Reviewed by: alc, kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D13423
It's theoretically possible for the vnode and object to be disassociated
while locks are dropped around the vget() call, in which case we
shouldn't proceed with laundering.
Noted and reviewed by: kib
MFC after: 1 week
The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.
Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.
Initially, only tag files that use BSD 4-Clause "Original" license.
RelNotes: yes
Differential Revision: https://reviews.freebsd.org/D13133
There is no NO_SWAPPING #ifdef left in the code.
Requested by: alc
Reviewed by: alc, markj
Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks
Differential revision: https://reviews.freebsd.org/D12663
Before r207410, the hold count of a page in a page queue was protected
by the queue lock, and, before laundering a page, the page daemon
removed managed writeable mappings of the page before releasing the
queue lock. This ensured that other threads could not concurrently
create transient writeable mappings using pmap_extract_and_hold() on a
user map, as is done for example by vmapbuf(). With that revision,
however, a race can allow the creation of such a mapping, meaning that
the page might be modified as it is being laundered, potentially
resulting in it being marked clean when its contents do not match
those given to the pager. Close the race by using the page lock to
synchronize the hold count check in vm_pageout_cluster() with the
removal of writeable managed mappings.
Reported by: alc
Reviewed by: alc, kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D12084
Decouple the pageout cluster size from the size of the hash table entry
used by the swap pager for mapping (object, pindex) to a block on the
swap device(s), and keep the size of a hash table entry at its current
size.
Eliminate a pointless macro.
Reviewed by: kib, markj (an earlier version)
MFC after: 4 weeks
Differential Revision: https://reviews.freebsd.org/D11305
in place. To do per-cpu stats, convert all fields that previously were
maintained in the vmmeters that sit in pcpus to counter(9).
- Since some vmmeter stats may be touched at very early stages of boot,
before we have set up UMA and we can do counter_u64_alloc(), provide an
early counter mechanism:
o Leave one spare uint64_t in struct pcpu, named pc_early_dummy_counter.
o Point counter(9) fields of vmmeter to pcpu[0].pc_early_dummy_counter,
so that at early stages of boot, before counters are allocated we already
point to a counter that can be safely written to.
o For sparc64 that required a whole dummy pcpu[MAXCPU] array.
Further related changes:
- Don't include vmmeter.h into pcpu.h.
- vm.stats.vm.v_swappgsout and vm.stats.vm.v_swappgsin changed to 64-bit,
to match kernel representation.
- struct vmmeter hidden under _KERNEL, and only vmstat(1) is an exclusion.
This is based on benno@'s 4-year old patch:
https://lists.freebsd.org/pipermail/freebsd-arch/2013-July/014471.html
Reviewed by: kib, gallatin, marius, lidl
Differential Revision: https://reviews.freebsd.org/D10156
A comment near kmem_reclaim() implies that we already did that.
Calling the hook is useful, because some handlers, e.g. ARC,
might be able to release significant amounts of KVA.
Now that we have more than one place where vm_lowmem hook is called,
use this change as an opportunity to introduce flags that describe
a reason for calling the hook. No handler makes use of the flags yet.
Reviewed by: markj, kib
MFC after: 1 week
Sponsored by: Panzura
Differential Revision: https://reviews.freebsd.org/D9764
There could be a race between the vm daemon setting RACCT_RSS based on
the vm space and vmspace_exit (called from exit1) resetting RACCT_RSS to
zero. In that case we can get a zombie process with non-zero RACCT_RSS.
If the process is jailed, that may break accounting for the jail.
There could be other consequences.
Fix this race in the vm daemon by updating RACCT_RSS only when a process
is in the normal state. Also, make accounting a little bit more
accurate by refreshing the page resident count after calling
vm_pageout_map_deactivate_pages().
Finally, add an assert that the RSS is zero when a process is reaped.
PR: 210315
Reviewed by: trasz
Differential Revision: https://reviews.freebsd.org/D9464
On systems without a configured swap device, an attempt to launder pages
from a swap object will always fail and result in the page being
reactivated. This means that the page daemon will continuously scan pages
that can never be evicted. With this change, anonymous pages are instead
moved to PQ_UNSWAPPABLE after a failed laundering attempt when no swap
devices are configured. PQ_UNSWAPPABLE is not scanned unless a swap device
is configured, so unreferenced unswappable pages are excluded from the page
daemon's workload.
Reviewed by: alc
The swap pager enqueues laundered pages near the head of the inactive queue
to avoid another trip through LRU before reclamation. This change adds
support for this behaviour to the vnode pager and makes use of it in UFS and
ext2fs. Some ioflag handling is consolidated into a common subroutine so
that this support can be easily extended to other filesystems which make use
of the buffer cache. No changes are needed for ZFS since its putpages
routine always undirties the pages before returning, and the laundry
thread requeues the pages appropriately in this case.
Reviewed by: alc, kib
Differential Revision: https://reviews.freebsd.org/D8589
pages, specificially, dirty pages that have passed once through the inactive
queue. A new, dedicated thread is responsible for both deciding when to
launder pages and actually laundering them. The new policy uses the
relative sizes of the inactive and laundry queues to determine whether to
launder pages at a given point in time. In general, this leads to more
intelligent swapping behavior, since the laundry thread will avoid pageouts
when the marginal benefit of doing so is low. Previously, without a
dedicated queue for dirty pages, the page daemon didn't have the information
to determine whether pageout provides any benefit to the system. Thus, the
previous policy often resulted in small but steadily increasing amounts of
swap usage when the system is under memory pressure, even when the inactive
queue consisted mostly of clean pages. This change addresses that issue,
and also paves the way for some future virtual memory system improvements by
removing the last source of object-cached clean pages, i.e., PG_CACHE pages.
The new laundry thread sleeps while waiting for a request from the page
daemon thread(s). A request is raised by setting the variable
vm_laundry_request and waking the laundry thread. We request launderings
for two reasons: to try and balance the inactive and laundry queue sizes
("background laundering"), and to quickly make up for a shortage of free
pages and clean inactive pages ("shortfall laundering"). When background
laundering is requested, the laundry thread computes the number of page
daemon wakeups that have taken place since the last laundering. If this
number is large enough relative to the ratio of the laundry and (global)
inactive queue sizes, we will launder vm_background_launder_target pages at
vm_background_launder_rate KB/s. Otherwise, the laundry thread goes back
to sleep without doing any work. When scanning the laundry queue during
background laundering, reactivated pages are counted towards the laundry
thread's target.
In contrast, shortfall laundering is requested when an inactive queue scan
fails to meet its target. In this case, the laundry thread attempts to
launder enough pages to meet v_free_target within 0.5s, which is the
inactive queue scan period.
A laundry request can be latched while another is currently being
serviced. In particular, a shortfall request will immediately preempt a
background laundering.
This change also redefines the meaning of vm_cnt.v_reactivated and removes
the functions vm_page_cache() and vm_page_try_to_cache(). The new meaning
of vm_cnt.v_reactivated now better reflects its name. It represents the
number of inactive or laundry pages that are returned to the active queue
on account of a reference.
In collaboration with: markj
Reviewed by: kib
Tested by: pho
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D8302
by vm_pageout_scan() local to vm_pageout_worker(). There is no reason
to store the pass in the NUMA domain structure.
Reviewed by: kib
MFC after: 3 weeks
target was met.
Previously, vm_pageout_worker() itself checked the length of the free page
queues to determine whether vm_pageout_scan(pass >= 1)'s inactive queue scan
freed enough pages to meet the free page target. Specifically,
vm_pageout_worker() used vm_paging_needed(). The trouble with
vm_paging_needed() is that it compares the length of the free page queues to
the wakeup threshold for the page daemon, which is much lower than the free
page target. Consequently, vm_pageout_worker() could conclude that the
inactive queue scan succeeded in meeting its free page target when in fact
it did not; and rather than immediately triggering an all-out laundering
pass over the inactive queue, vm_pageout_worker() would go back to sleep
waiting for the free page count to fall below the page daemon wakeup
threshold again, at which point it will perform another limited (pass == 1)
scan over the inactive queue.
Changing vm_pageout_worker() to use vm_page_count_target() instead of
vm_paging_needed() won't work because any page allocations that happen
concurrently with the inactive queue scan will result in the free page count
being below the target at the end of a successful scan. Instead, having
vm_pageout_scan() return a value indicating success or failure is the most
straightforward fix.
Reviewed by: kib, markj
MFC after: 3 weeks
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D8111
In particular, fix factual, grammatical, and spelling errors in various
comments, and remove comments that are out of place in this function.
Reviewed by: kib, markj
MFC after: 3 weeks
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D7410
to r254304, we had separate functions for reclamation and laundering
(vm_pageout_scan) versus updating usage information, i.e., "reference
bits", on active pages (vm_pageout_page_stats), and we only performed
vm_req_vmdaemon(VM_SWAP_IDLE) if vm_pages_needed was true. However, since
r254303, if vm_swap_idle_enabled was "1", we have performed
vm_req_vmdaemon(VM_SWAP_IDLE) regardless of whether we are short of free
pages. This was unintended and too aggressive, so I suspect no one uses
this feature. With this change, we restore the historical behavior and
only perform vm_req_vmdaemon(VM_SWAP_IDLE) when we are short of free
pages.
Reviewed by: kib, markj
It's a threshold for v_free_count, which is of type u_int. This also lets
us get rid of a cast in vm_paging_needed().
Reviewed by: alc
MFC after: 1 week
There is an order between covered vnode lock and allproc_lock, which
is established by calling mountcheckdirs() while owning the covered
vnode lock. mountcheckdirs() iterates over the processes, protected by
allproc_lock. This order is needed and seems to be not avoidable.
On the other hand, various VM daemons also need to iterate over all
processes, and they lock and unlock user maps. Since unlock of the
user map may trigger processing of the deferred map entries, it causes
vnode locking to occur. Or, when vmspace is freed, dropping references
on the vnode-backed object also lock vnodes. We get reverted order
comparing with the mount/unmount order.
For VM daemons, there is no need to own allproc_lock while we operate
on vmspaces. If the process is held, it serves as the marker for
allproc list, which allows to continue the iteration.
Add _PHOLD_LITE() macro, similar to _PHOLD(), but not causing swap-in
of the kernel stacks. It is used instead of _PHOLD() in vm code,
since e.g. calling faultin() in OOM conditions only exaggerates the
problem.
Modernize comment describing PHOLD.
Reported by: lists@yamagi.org
Tested by: pho (previous version)
Reviewed by: jhb
Sponsored by: The FreeBSD Foundation
MFC after: 3 week
Approved by: re (gjb)
Differential revision: https://reviews.freebsd.org/D6679
indicate that threads are waiting for free pages to become available and
(2) to indicate whether a wakeup call has been sent to the page daemon.
The trouble is that a single flag cannot really serve both purposes, because
we have two distinct targets for when to wakeup threads waiting for free
pages versus when the page daemon has completed its work. In particular,
the flag will be cleared by vm_page_free() before the page daemon has met
its target, and this can lead to the OOM killer being invoked prematurely.
To address this problem, a new flag "vm_pageout_wanted" is introduced.
Discussed with: jeff
Reviewed by: kib, markj
Tested by: markj
Sponsored by: EMC / Isilon Storage Division
