includes the latter, but also declares variables which are defined
in kern/subr_param.c).
Change som VM parameters from quad_t to unsigned long. They refer to
quantities (size limits for text, heap and stack segments) which must
necessarily be smaller than the size of the address space, so long is
adequate on all platforms.
MFC after: 1 week
number of entries into bucket_zone_lookup(), which helps make more
clear the logic of consumers of bucket zones.
Annotate the behavior of bucket_init() with a comment indicating
how the various data structures, including the bucket lookup tables,
are initialized.
swapoff: failed to locate %d swap blocks
The race occurred because putpages() can block between the time it
allocates swap space and the time it updates the swap metadata to
associate that space with a vm_object, so swapoff() would complain
about the temporary inconsistency. I hoped to fix this by making
swp_pager_getswapspace() and swp_pager_meta_build() a single atomic
operation, but that proved to be inconvenient. With this change,
swapoff() simply doesn't attempt to be so clever about detecting when
all the pageout activity to the target device should have drained.
because this call is only needed to wake threads that slept when they
discovered a dead object connected to a vnode. To eliminate unnecessary
calls to wakeup() by vnode_pager_dealloc(), introduce a new flag,
OBJ_DISCONNECTWNT.
Reviewed by: tegge@
thread is created rather than adjusting the priority in the main
function. (kthread_create() should probably take the initial priority
as an argument.)
- Only yield the CPU in the !PREEMPTION case if there are any other
runnable threads. Yielding when there isn't anything else better to do
just wastes time in pointless context switches (albeit while the system
is idle.)
In order to avoid livelock, swapoff() skips over objects with a
nonzero pip count and makes another pass if necessary. Since it is
impossible to know which objects we care about, it would choose an
arbitrary object with a nonzero pip count and wait for it before
making another pass, the theory being that this object would finish
paging about as quickly as the ones we care about. Unfortunately,
we may have slept since we acquired a reference to this object.
Hack around this problem by tsleep()ing on the pointer anyway, but
timeout after a fixed interval. More elegant solutions are possible,
but the ones I considered unnecessarily complicate this rare case.
Also, kill some nits that seem to have crept into the swapoff() code
in the last 75 revisions or so:
- Don't pass both sp and sp->sw_used to swap_pager_swapoff(), since
the latter can be derived from the former.
- Replace swp_pager_find_dev() with something simpler. There's no
need to iterate over the entire list of swap devices just to determine
if a given block is assigned to the one we're interested in.
- Expand the scope of the swhash_mtx in a couple of places so that it
isn't released and reacquired once for every hash bucket.
- Don't drop the swhash_mtx while holding a reference to an object.
We need to lock the object first. Unfortunately, doing so would
violate the established lock order, so use VM_OBJECT_TRYLOCK() and
try again on a subsequent pass if the object is already locked.
- Refactor swp_pager_force_pagein() and swap_pager_swapoff() a bit.
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.
IF INVARIANTS is defined, and in the rare case that we have
allocated some objects from the slab and at least one initializer
on at least one of those objects failed, and we need to fail the
allocation and push the uninitialized items back into the slab
caches -- in that scenario, we would fail to [re]set the
bucket cache's ub_bucket item references to NULL, which would
eventually trigger a KASSERT.
We keep si_bsize_phys around for now as that is the simplest way to pull
the number out of disk device drivers in devfs_open(). The correct solution
would be to do an ioctl(DIOCGSECTORSIZE), but the point is probably mooth
when filesystems sit on GEOM, so don't bother for now.
Extend it with a strategy method.
Add bufstrategy() which do the usual VOP_SPECSTRATEGY/VOP_STRATEGY
song and dance.
Rename ibwrite to bufwrite().
Move the two NFS buf_ops to more sensible places, add bufstrategy
to them.
Add inlines for bwrite() and bstrategy() which calls through
buf->b_bufobj->b_ops->b_{write,strategy}().
Replace almost all VOP_STRATEGY()/VOP_SPECSTRATEGY() calls with bstrategy().
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.)
that indicates that the caller does not want a page with its busy flag set.
In many places, the global page queues lock is acquired and released just
to clear the busy flag on a just allocated page. Both the allocation of
the page and the clearing of the busy flag occur while the containing vm
object is locked. So, the busy flag might as well never be set.
Initialize b_bufobj for all buffers.
Make incore() and gbincore() take a bufobj instead of a vnode.
Make inmem() local to vfs_bio.c
Change a lot of VI_[UN]LOCK(bp->b_vp) to BO_[UN]LOCK(bp->b_bufobj)
also VI_MTX() to BO_MTX(),
Make buf_vlist_add() take a bufobj instead of a vnode.
Eliminate other uses of bp->b_vp where bp->b_bufobj will do.
Various minor polishing: remove "register", turn panic into KASSERT,
use new function declarations, TAILQ_FOREACH_SAFE() etc.
Add bufobj_wref(), bufobj_wdrop() and bufobj_wwait() to handle the write
count on a bufobj. Bufobj_wdrop() replaces vwakeup().
Use these functions all relevant places except in ffs_softdep.c where
the use if interlocked_sleep() makes this impossible.
Rename b_vnbufs to b_bobufs now that we touch all the relevant files anyway.
errors are in rarely executed paths.
1. Each time the retry_alloc path is taken, the PG_BUSY must be set again.
Otherwise vm_page_remove() panics.
2. There is no need to set PG_BUSY on the newly allocated page before
freeing it. The page already has PG_BUSY set by vm_page_alloc().
Setting it again could cause an assertion failure.
MFC after: 2 weeks
vm_page_io_finish(). The motivation being to transition synchronization of
the vm_page's busy field from the global page queues lock to the per-object
lock.
sysctl routines and state. Add some code to use it for signalling the need
to downconvert a data structure to 32 bits on a 64 bit OS when requested by
a 32 bit app.
I tried to do this in a generic abi wrapper that intercepted the sysctl
oid's, or looked up the format string etc, but it was a real can of worms
that turned into a fragile mess before I even got it partially working.
With this, we can now run 'sysctl -a' on a 32 bit sysctl binary and have
it not abort. Things like netstat, ps, etc have a long way to go.
This also fixes a bug in the kern.ps_strings and kern.usrstack hacks.
These do matter very much because they are used by libc_r and other things.
state management corruption, mbuf leaks, general mbuf corruption,
and at least on i386 a first level splash damage radius that
encompasses up to about half a megabyte of the memory after
an mbuf cluster's allocation slab. In short, this has caused
instability nightmares anywhere the right kind of network traffic
is present.
When the polymorphic refcount slabs were added to UMA, the new types
were not used pervasively. In particular, the slab management
structure was turned into one for refcounts, and one for non-refcounts
(supposed to be mostly like the old slab management structure),
but the latter was almost always used through out. In general, every
access to zones with UMA_ZONE_REFCNT turned on corrupted the
"next free" slab offset offset and the refcount with each other and
with other allocations (on i386, 2 mbuf clusters per 4096 byte slab).
Fix things so that the right type is used to access refcounted zones
where it was not before. There are additional errors in gross
overestimation of padding, it seems, that would cause a large kegs
(nee zones) to be allocated when small ones would do. Unless I have
analyzed this incorrectly, it is not directly harmful.
frobbing the cdevsw.
In both cases we examine only the cdevsw and it is a good question if we
weren't better off copying those properties into the cdev in the first
place. This question will be revisited.
UMA_ZONE_NOFREE to guarantee type stability, so proc_fini() should
never be called. Move an assertion from proc_fini() to proc_dtor()
and garbage-collect the rest of the unreachable code. I have retained
vm_proc_dispose(), since I consider its disuse a bug.
and which takes a M_WAITOK/M_NOWAIT flag argument.
Add compatibility isa_dmainit() macro which whines loudly if
isa_dma_init() fails.
Problem uncovered by: tegge
write and zero-fill faults to run without holding Giant. It is still
possible to disable Giant-free operation by setting debug.mpsafevm to 0 in
loader.conf.
FULL_PREEMPTION is defined. Add a runtime warning to ULE if PREEMPTION is
enabled (code inspired by the PREEMPTION warning in kern_switch.c). This
is a possible MT5 candidate.
page zeroing thread before it has been created. It was possible for
calls to free() very early in the boot process to panic here because
the sleep queues were not yet initialised. Specifically, sysinit_add()
running at SI_SUB_KLD would trigger this if the array of pointers
became big enough to require uma_large_alloc() allocations.
Submitted by: peter
position that is 64-bit aligned and makes sure that the valid and
dirty fields are also 64-bit aligned. This means that if PAGE_SIZE
is 32K, the size of the vm_page structure is only increased by 8
bytes instead of 16 bytes. More importantly, the vm_page structure
is either 120 or 128 bytes on ia64. These are "interesting" sizes.
manipulating a vnode, e.g., calling vput(). This reduces contention for
Giant during many copy-on-write faults, resulting in some additional
speedup on SMPs.
Note: debug_mpsafevm must be enabled for this optimization to take effect.
"debug.mpsafevm" results in (almost) Giant-free execution of zero-fill
page faults. (Giant is held only briefly, just long enough to determine
if there is a vnode backing the faulting address.)
Also, condition the acquisition and release of Giant around calls to
pmap_remove() on "debug.mpsafevm".
The effect on performance is significant. On my dual Opteron, I see a
3.6% reduction in "buildworld" time.
- Use atomic operations to update several counters in vm_fault().
wait for system wires to disappear, do so (much more trivially) by
instead only checking for system wires of user maps and not kernel maps.
Alternative by: tor
Reviewed by: alc
algorithm built into the map entry splay tree. This replaces the
first_free hint in struct vm_map with two fields in vm_map_entry:
adj_free, the amount of free space following a map entry, and
max_free, the maximum amount of free space in the entry's subtree.
These fields make it possible to find a first-fit free region of a
given size in one pass down the tree, so O(log n) amortized using
splay trees.
This significantly reduces the overhead in vm_map_findspace() for
applications that mmap() many hundreds or thousands of regions, and
has a negligible slowdown (0.1%) on buildworld. See, for example, the
discussion of a micro-benchmark titled "Some mmap observations
compared to Linux 2.6/OpenBSD" on -hackers in late October 2003.
OpenBSD adopted this approach in March 2002, and NetBSD added it in
November 2003, both with Red-Black trees.
Submitted by: Mark W. Krentel
to avoid later changes before pmap_enter() and vm_fault_prefault()
has completed.
Simplify deadlock avoidance by not blocking on vm map relookup.
In collaboration with: alc
* Allow no-fault wiring/unwiring to succeed for consistency;
however, the wired count remains at zero, so it's a special case.
* Fix issues inside vm_map_wire() and vm_map_unwire() where the
exact state of user wiring (one or zero) and system wiring
(zero or more) could be confused; for example, system unwiring
could succeed in removing a user wire, instead of being an
error.
* Require all mappings to be unwired before they are deleted.
When VM space is still wired upon deletion, it will be waited
upon for the following unwire. This makes vslock(9) work
rather than allowing kernel-locked memory to be deleted
out from underneath of its consumer as it would before.
1. Move a comment to its proper place, updating it. (Except for white-
space, this comment had been unchanged since revision 1.1!)
2. Remove spl calls.
should be set to VM_PAGE_BITS_ALL before returning, to ensure that
neither vm_pager_get_pages nor vm_fault calls vm_page_zero_invalid
after dev_pager_getpages has returned.
Submitted by: tegge
so that they know whether the allocation is supposed to be able to sleep
or not.
* Allow uma_zone constructors and initialation functions to return either
success or error. Almost all of the ones in the tree currently return
success unconditionally, but mbuf is a notable exception: the packet
zone constructor wants to be able to fail if it cannot suballocate an
mbuf cluster, and the mbuf allocators want to be able to fail in general
in a MAC kernel if the MAC mbuf initializer fails. This fixes the
panics people are seeing when they run out of memory for mbuf clusters.
* Allow debug.nosleepwithlocks on WITNESS to be disabled, without changing
the default.
Both bmilekic and jeff have reviewed the changes made to make failable
zone allocations work.
those architectures without pmap locking.
- Eliminate the acquisition and release of Giant from vm_map_protect().
(Translation: mprotect(2) runs to completion without touching Giant on
alpha, amd64, i386 and ia64.)
maps. We always acquire the sx lock exclusively here, but we can't
use a mutex because we want to be able to sleep while holding the
lock. This is completely equivalent to what we were doing with the
lockmgr(9) locks before.
Approved by: alc
- Enable recursion on the page queues lock. This allows calls to
vm_page_alloc(VM_ALLOC_NORMAL) and UMA's obj_alloc() with the page
queues lock held. Such calls are made to allocate page table pages
and pv entries.
- The previous change enables a partial reversion of vm/vm_page.c
revision 1.216, i.e., the call to vm_page_alloc() by vm_page_cowfault()
now specifies VM_ALLOC_NORMAL rather than VM_ALLOC_INTERRUPT.
- Add partial locking to pmap_copy(). (As a side-effect, pmap_copy()
should now be faster on i386 SMP because it no longer generates IPIs
for TLB shootdown on the other processors.)
- Complete the locking of pmap_enter() and pmap_enter_quick(). (As of now,
all changes to a user-level pmap on alpha, amd64, and i386 are performed
with appropriate locking.)
- zone_large_init() stays pretty much the same.
- zone_small_init() will try to stash the slab header in the slab page
being allocated if the amount of calculated wasted space is less
than UMA_MAX_WASTE (for both the UMA_ZONE_REFCNT case and regular
case). If the amount of wasted space is >= UMA_MAX_WASTE, then
UMA_ZONE_OFFPAGE will be set and the slab header will be allocated
separately for better use of space.
- uma_startup() calculates the maximum ipers required in offpage slabs
(so that the offpage slab header zone(s) can be sized accordingly).
The algorithm used to calculate this replaces the old calculation
(which only happened to work coincidentally). We now iterate over
possible object sizes, starting from the smallest one, until we
determine that wastedspace calculated in zone_small_init() might
end up being greater than UMA_MAX_WASTE, at which point we use the
found object size to compute the maximum possible ipers. The
reason this works is because:
- wastedspace versus objectsize is a see-saw function with
local minima all equal to zero and local maxima growing
directly proportioned to objectsize. This implies that
for objects up to or equal a certain objectsize, the see-saw
remains entirely below UMA_MAX_WASTE, so for those objectsizes
it is impossible to ever go OFFPAGE for slab headers.
- ipers (items-per-slab) versus objectsize is an inversely
proportional function which falls off very quickly (very large
for small objectsizes).
- To determine the maximum ipers we'll ever need from OFFPAGE
slab headers we first find the largest objectsize for which
we are guaranteed to not go offpage for and use it to compute
ipers (as though we were offpage). Since the only objectsizes
allowed to go offpage are bigger than the found objectsize,
and since ipers vs objectsize is inversely proportional (and
monotonically decreasing), then we are guaranteed that the
ipers computed is always >= what we will ever need in offpage
slab headers.
- Define UMA_FRITM_SZ and UMA_FRITMREF_SZ to be the actual (possibly
padded) size of each freelist index so that offset calculations are
fixed.
This might fix weird data corruption problems and certainly allows
ARM to now boot to at least single-user (via simulator).
Tested on i386 UP by me.
Tested on sparc64 SMP by fenner.
Tested on ARM simulator to single-user by cognet.
vm/vm_object.c revision 1.88) and vm_object_sync() (originating in
vm/vm_map.c revision 1.36): When descending a chain of backing objects,
both use the wrong object's backing offset. Consequently, both may
operate on the wrong pages.
Quoting Matt, "This could be responsible for all of the sporatic madvise
oddness that has been reported over the years."
Reviewed by: Matt Dillon
- Push down Giant into shmexit(). (Giant is acquired only if the vmspace
contains shm segments.)
- Eliminate the acquisition of Giant from proc_rwmem().
- Reduce the scope of Giant in exit1(), uncovering the destruction of the
address space.
vmspace to the new vmspace in vmspace_exec() is mostly wasted effort. With
one exception, vm_swrss, the copied fields are immediately overwritten.
Instead, initialize these fields to zero in vmspace_alloc(), eliminating a
bcopy() from vmspace_exec() and a bzero() from vmspace_fork().
kmem_alloc_pageable(). The difference between these is that an errant
memory access to the zone will be detected sooner with
kmem_alloc_nofault().
The following changes serve to eliminate the following lock-order
reversal reported by witness:
1st 0xc1a3c084 vm object (vm object) @ vm/swap_pager.c:1311
2nd 0xc07acb00 swap_pager swhash (swap_pager swhash) @ vm/swap_pager.c:1797
3rd 0xc1804bdc vm object (vm object) @ vm/uma_core.c:931
There is no potential deadlock in this case. However, witness is unable
to recognize this because vm objects used by UMA have the same type as
ordinary vm objects. To remedy this, we make the following changes:
- Add a mutex type argument to VM_OBJECT_LOCK_INIT().
- Use the mutex type argument to assign distinct types to special
vm objects such as the kernel object, kmem object, and UMA objects.
- Define a static swap zone object for use by UMA. (Only static
objects are assigned a special mutex type.)
being incomplete, it currently has to know how to drop and pick back
up the vm_object's mutex if it has to sleep and drop the page queue
mutex. The problem with this is that if the page is busy, while we
are sleeping, the page can be freed and object disappear. When trying
to lock m->object, we'd get a stale or NULL pointer and crash.
The object is now cached, but this makes the assumption that
the object is referenced in some manner and will not itself
disappear while it is unlocked. Since this only happens if
the object is locked, I had to remove an assumption earlier in
contigmalloc() that reversed the order of locking the object and
doing vm_page_sleep_if_busy(), not the normal order.
init and fini handlers. Our vm system removes all userland mappings at
exit prior to calling pmap_release. It just so happens that we might
as well reuse the pmap for the next process since the userland slate
has already been wiped clean.
However. There is a functional benefit to this as well. For platforms
that share userland and kernel context in the same pmap, it means that
the kernel portion of a pmap remains valid after the vmspace has been
freed (process exit) and while it is in uma's cache. This is significant
for i386 SMP systems with kernel context borrowing because it avoids
a LOT of IPIs from the pmap_lazyfix() cleanup in the usual case.
Tested on: amd64, i386, sparc64, alpha
Glanced at by: alc
