some time ago. The mistake was to check that the page was not
referenced since the last active scan before moving it to inactive.
Now we just clear reference and move it to inacive (which is where
the second clock hand sweep occurs).
the mapping is:
VM_PAGER_OK 0
VM_PAGER_BAD <unused>
VM_PAGER_FAIL <unused>
VM_PAGER_PEND 0 (see below)
VM_PAGER_ERROR EIO
VM_PAGER_AGAIN EAGAIN
VM_PAGER_UNLOCK EBUSY
VM_PAGER_REFAULT ERESTART
for async i/o requests, it used to be possible for the request to
be convert to sync, and the pager would return VM_PAGER_OK or VM_PAGER_PEND
to indicate whether the caller should perform post-i/o cleanup.
this is no longer allowed; pagers must now return 0 to indicate that
the async i/o was successfully started, and the caller never needs to
worry about doing the post-i/o cleanup.
each of the basic types (anonymous data, executable image, cached files)
and prevent the pagedaemon from reusing a given page if that would reduce
the count of that type of page below a sysctl-setable minimum threshold.
the thresholds are controlled via three new sysctl tunables:
vm.anonmin, vm.vnodemin, and vm.vtextmin. these tunables are the
percentages of pageable memory reserved for each usage, and we do not allow
the sum of the minimums to be more than 95% so that there's always some
memory that can be reused.
Mach VM's now. Specific changes:
- Pages now need not have all of their mappings removed before being
put on the inactive list. They only need to have the "referenced"
attribute cleared. This makes putting pages onto the inactive list
much more efficient. In order to eliminate redundant clearings of
"refrenced", callers of uvm_pagedeactivate() must now do this
themselves.
- When checking the "modified" attribute for a page (for clearing
PG_CLEAN), make sure to only do it if PG_CLEAN is currently set on
the page (saves a potentially expensive pmap operation).
- When scanning the inactive list, if a page is referenced, reactivate
it (this part was actually added in uvm_pdaemon.c,v 1.27). This
now works properly now that pages on the inactive list are allowed to
have mappings.
- When scanning the inactive list and considering a page for freeing,
remove all mappings, and then check the "modified" attribute if the
page is marked PG_CLEAN.
- When scanning the active list, if the page was referenced since its
last sweep by the scanner, don't deactivate it. (This part was
actually added in uvm_pdaemon.c,v 1.28.)
These changes greatly improve interactive performance during
moderate to high memory and I/O load.
When it wasn't (which could happen on a 4Mb machine with 32kb pages),
uvm_pagealloc_strat could refuse to allocate user memory, while the pagedaemon
didn't think it was worth freeing any more, resulting in the system seizing up.
<vm/pglist.h> -> <uvm/uvm_pglist.h>
<vm/vm_inherit.h> -> <uvm/uvm_inherit.h>
<vm/vm_kern.h> -> into <uvm/uvm_extern.h>
<vm/vm_object.h> -> nothing
<vm/vm_pager.h> -> into <uvm/uvm_pager.h>
also includes a bunch of <vm/vm_page.h> include removals (due to redudancy
with <vm/vm.h>), and a scattering of other similar headers.
level directly, instead of making the caller wrap the calls in
splimp()/splx().
- Add a comment documenting that interrupts that cause memory allocation
must be blocked while the free page queue is locked.
Since interrupts must be blocked while this lock is asserted, tying them
together like this helps to prevent mistakes.
numerous pagedaemon improvements were needed to make this useful:
- don't bother waking up procs waiting for memory if there's none to be had.
- start 4 times as many pageouts as we need free pages.
this should reduce latency in low-memory situations.
- in inactive scanning, if we find dirty swap-backed pages when swap space
is full of non-resident pages, reactivate some number of these to flush
less active pages to the inactive queue so we can consider paging them out.
this replaces the previous scheme of inactivating pages beyond the
inactive target when we failed to free anything during inactive scanning.
- during both active and inactive scanning, free any swap resources from
dirty swap-backed pages if swap space is full. this allows other pages
be paged out into that swap space.
UVM was written by chuck cranor <chuck@maria.wustl.edu>, with some
minor portions derived from the old Mach code. i provided some help
getting swap and paging working, and other bug fixes/ideas. chuck
silvers <chuq@chuq.com> also provided some other fixes.
this is the UVM kernel code portion.
this will be KNF'd shortly. :-)
chs