represented a write access that is allowed to override write protection.
Until now, VM_PROT_OVERRIDE_WRITE has been used to write breakpoints into
text pages. Text pages are not just write protected but they are also
copy-on-write. VM_PROT_OVERRIDE_WRITE overrides the write protection on the
text page and triggers the replication of the page so that the breakpoint
will be written to a private copy. However, here is where things become
confused. It is the debugger, not the process being debugged that requires
write access to the copied page. Nonetheless, the copied page is being
mapped into the process with write access enabled. In other words, once the
debugger sets a breakpoint within a text page, the program can write to its
private copy of that text page. Whereas prior to setting the breakpoint, a
SIGSEGV would have occurred upon a write access. VM_PROT_COPY addresses
this problem. The combination of VM_PROT_READ and VM_PROT_COPY forces the
replication of a copy-on-write page even though the access is only for read.
Moreover, the replicated page is only mapped into the process with read
access, and not write access.
Reviewed by: kib
MFC after: 4 weeks
pages.
(Note: Claims made in the comments about the handling of breakpoints in
wired pages have been false for roughly a decade. This and another bug
involving breakpoints will be fixed in coming changes.)
Reviewed by: kib
version of this file. When a process forks, any wired pages are immediately
copied because copy-on-write is not supported for wired pages. In other
words, the child process is given its own private copy of each wired page
from its parent's address space. Unfortunately, to date, these copied pages
have been mapped into the child's address space with the wrong permissions,
typically VM_PROT_ALL. This change corrects the permissions.
Reviewed by: kib
install new shadow object behind the map entry and copy the pages
from the underlying objects to it. This makes the mprotect(2) call to
actually perform the requested operation instead of silently do nothing
and return success, that causes SIGSEGV on later write access to the
mapping.
Reuse vm_fault_copy_entry() to do the copying, modifying it to behave
correctly when src_entry == dst_entry.
Reviewed by: alc
MFC after: 3 weeks
a device pager (OBJT_DEVICE) object in that it uses fictitious pages to
provide aliases to other memory addresses. The primary difference is that
it uses an sglist(9) to determine the physical addresses for a given offset
into the object instead of invoking the d_mmap() method in a device driver.
Reviewed by: alc
Approved by: re (kensmith)
MFC after: 2 weeks
charge the objects created by vm_fault_copy_entry. The object charge
was set, but reserve not incremented.
Reported by: Greg Rivers <gcr+freebsd-current tharned org>
Reviewed by: alc (previous version)
Approved by: re (kensmith)
rlimit RLIMIT_SWAP that limits the amount of swap that may be reserved
for the uid.
The accounting information (charge) is associated with either map entry,
or vm object backing the entry, assuming the object is the first one
in the shadow chain and entry does not require COW. Charge is moved
from entry to object on allocation of the object, e.g. during the mmap,
assuming the object is allocated, or on the first page fault on the
entry. It moves back to the entry on forks due to COW setup.
The per-entry granularity of accounting makes the charge process fair
for processes that change uid during lifetime, and decrements charge
for proper uid when region is unmapped.
The interface of vm_pager_allocate(9) is extended by adding struct ucred *,
that is used to charge appropriate uid when allocation if performed by
kernel, e.g. md(4).
Several syscalls, among them is fork(2), may now return ENOMEM when
global or per-uid limits are enforced.
In collaboration with: pho
Reviewed by: alc
Approved by: re (kensmith)
busy count. Only mappings that allow write access should be prevented by
a non-zero busy count.
(The prohibition on mapping pages for read access when they have a non-
zero busy count originated in revision 1.202 of i386/i386/pmap.c when
this code was a part of the pmap.)
Reviewed by: tegge
fault. In r188331 this update was relocated because of synchronization
changes to a place where it would occur on both hard and soft faults. This
change again restricts the update to hard faults.
acquire vnode lock for OBJT_VNODE object after map lock is dropped.
Because we have the busy page(s) in the object, sleeping there would
result in deadlock with vnode resize. Try to get lock without sleeping,
and, if the attempt failed, drop the state, lock the vnode, and restart
the fault handler from the start with already locked vnode.
Because the vnode_pager_lock() function is inlined in vm_fault(),
axe it.
Based on suggestion by: alc
Reviewed by: tegge, alc
Tested by: pho
Instead of checking each page for PG_UNMANAGED, perform a one-time
check whether the object is OBJT_PHYS. (PG_UNMANAGED pages only
belong to OBJT_PHYS objects.)
Specifically, since the delete-behind heuristic is never applied to a
device-backed object, there is no point in checking whether each of the
object's pages is fictitious. (Only device-backed objects have
fictitious pages.)
machine-independent support for superpages. (The earlier part was
the rewrite of the physical memory allocator.) The remainder of the
code required for superpages support is machine-dependent and will
be added to the various pmap implementations at a later date.
Initially, I am only supporting one large page size per architecture.
Moreover, I am only enabling the reservation system on amd64. (In
an emergency, it can be disabled by setting VM_NRESERVLEVELS to 0
in amd64/include/vmparam.h or your kernel configuration file.)
ways:
(1) Cached pages are no longer kept in the object's resident page
splay tree and memq. Instead, they are kept in a separate per-object
splay tree of cached pages. However, access to this new per-object
splay tree is synchronized by the _free_ page queues lock, not to be
confused with the heavily contended page queues lock. Consequently, a
cached page can be reclaimed by vm_page_alloc(9) without acquiring the
object's lock or the page queues lock.
This solves a problem independently reported by tegge@ and Isilon.
Specifically, they observed the page daemon consuming a great deal of
CPU time because of pages bouncing back and forth between the cache
queue (PQ_CACHE) and the inactive queue (PQ_INACTIVE). The source of
this problem turned out to be a deadlock avoidance strategy employed
when selecting a cached page to reclaim in vm_page_select_cache().
However, the root cause was really that reclaiming a cached page
required the acquisition of an object lock while the page queues lock
was already held. Thus, this change addresses the problem at its
root, by eliminating the need to acquire the object's lock.
Moreover, keeping cached pages in the object's primary splay tree and
memq was, in effect, optimizing for the uncommon case. Cached pages
are reclaimed far, far more often than they are reactivated. Instead,
this change makes reclamation cheaper, especially in terms of
synchronization overhead, and reactivation more expensive, because
reactivated pages will have to be reentered into the object's primary
splay tree and memq.
(2) Cached pages are now stored alongside free pages in the physical
memory allocator's buddy queues, increasing the likelihood that large
allocations of contiguous physical memory (i.e., superpages) will
succeed.
Finally, as a result of this change long-standing restrictions on when
and where a cached page can be reclaimed and returned by
vm_page_alloc(9) are eliminated. Specifically, calls to
vm_page_alloc(9) specifying VM_ALLOC_INTERRUPT can now reclaim and
return a formerly cached page. Consequently, a call to malloc(9)
specifying M_NOWAIT is less likely to fail.
Discussed with: many over the course of the summer, including jeff@,
Justin Husted @ Isilon, peter@, tegge@
Tested by: an earlier version by kris@
Approved by: re (kensmith)
1. Rewrite the backward scan. Specifically, reverse the order in which
pages are allocated so that upon failure it is never necessary to
free pages that were just allocated. Moreover, any allocated pages
can be put to use. This makes the backward scan behave just like the
forward scan.
2. Eliminate an explicit, unsynchronized check for low memory before
calling vm_page_alloc(). It serves no useful purpose. It is, in
effect, optimizing the uncommon case at the expense of the common
case.
Approved by: re (hrs)
MFC after: 3 weeks
vm_fault_additional_pages() that was introduced in revision 1.47. Then
as now, it is unnecessary because dev_pager_haspage() returns zero for
both the number of pages to read ahead and read behind, producing the
same exact behavior by vm_fault_additional_pages() as the special case
handling.
Approved by: re (rwatson)
tracks the total number of reactivated pages. (We have not been
counting reactivations by vm_fault() since revision 1.46.)
Correct a comment in vm_fault_additional_pages().
Approved by: re (kensmith)
MFC after: 1 week
- Rename PCPU_LAZY_INC into PCPU_INC
- Add the PCPU_ADD interface which just does an add on the pcpu member
given a specific value.
Note that for most architectures PCPU_INC and PCPU_ADD are not safe.
This is a point that needs some discussions/work in the next days.
Reviewed by: alc, bde
Approved by: jeff (mentor)
td_ru. This removes the requirement for per-process synchronization in
statclock() and mi_switch(). This was previously supported by
sched_lock which is going away. All modifications to rusage are now
done in the context of the owning thread. reads proceed without locks.
- Aggregate exiting threads rusage in thread_exit() such that the exiting
thread's rusage is not lost.
- Provide a new routine, rufetch() to fetch an aggregate of all rusage
structures from all threads in a process. This routine must be used
in any place requiring a rusage from a process prior to it's exit. The
exited process's rusage is still available via p_ru.
- Aggregate tick statistics only on demand via rufetch() or when a thread
exits. Tick statistics are kept in the thread and protected by sched_lock
until it exits.
Initial patch by: attilio
Reviewed by: attilio, bde (some objections), arch (mostly silent)
Probabilly, a general approach is not the better solution here, so we should
solve the sched_lock protection problems separately.
Requested by: alc
Approved by: jeff (mentor)
vm_map_pmap_enter() unless the caller is madvise(MADV_WILLNEED). With
the exception of calls to vm_map_pmap_enter() from
madvise(MADV_WILLNEED), vm_fault_prefault() and vm_map_pmap_enter()
are both used to create speculative mappings. Thus, always
reactivating cached pages is a mistake. In principle, cached pages
should only be reactivated by an actual access. Otherwise, the
following misbehavior can occur. On a hard fault for a text page the
clustering algorithm fetches not only the required page but also
several of the adjacent pages. Now, suppose that one or more of the
adjacent pages are never accessed. Ultimately, these unused pages
become cached pages through the efforts of the page daemon. However,
the next activation of the executable reactivates and maps these
unused pages. Consequently, they are never replaced. In effect, they
become pinned in memory.
vmcnts. This can be used to abstract away pcpu details but also changes
to use atomics for all counters now. This means sched lock is no longer
responsible for protecting counts in the switch routines.
Contributed by: Attilio Rao <attilio@FreeBSD.org>
The problem is this: vm_fault_additional_pages() calls vm_pager_has_page(),
which calls vnode_pager_haspage(). Now when VOP_BMAP() returns an error (eg.
EOPNOTSUPP), vnode_pager_haspage() returns TRUE without initializing 'before'
and 'after' arguments, so we have some accidental values there. This bascially
was causing this condition to be meet:
if ((rahead + rbehind) >
((cnt.v_free_count + cnt.v_cache_count) - cnt.v_free_reserved)) {
pagedaemon_wakeup();
[...]
}
(we have some random values in rahead and rbehind variables)
I'm not entirely sure this is the right fix, maybe we should just return FALSE
in vnode_pager_haspage() when VOP_BMAP() fails?
alc@ knows about this problem, maybe he will be able to come up with a better
fix if this is not the right one.
page queues-synchronized flag. Reduce the scope of the page queues lock in
vm_fault() accordingly.
Move vm_fault()'s call to vm_object_set_writeable_dirty() outside of the
scope of the page queues lock. Reviewed by: tegge
Additionally, eliminate an unnecessary dereference in computing the
argument that is passed to vm_object_set_writeable_dirty().
There is a race with the current locking scheme and removing
it should have no measurable performance impact.
This fixes page faults leading to panics in pmap_enter_quick_locked()
on amd64/i386.
Reviewed by: alc,jhb,peter,ps
