bits, by storing and modifying the complement of the original leaf
mask, and by avoiding some unnecessary intermediate variables in
computing the shift amounts. The logic is similar to what has recently
been committed to sys/sys/bitstring.h.
Compute better hint updates for the case when the cursor starts in
mid-leaf, and eliminates some otherwise viable solutions. Assume the
worst case, that all the eliminated offsets could have been solutions,
and you can still compute a better hint than we use now.
Eliminate some unnecessary conditional control flow.
Approved by: alc
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D22666
if a retry to allocate swap space, after a larger allocation attempt failed, allocated a smaller set of free blocks
that ended on a 32- or 64-block boundary.
Add tests to detect this kind of failure-to-extend-at-boundary and prevent the associated accounting screwup.
Reported by: pho
Tested by: pho
Reviewed by: alc
Approved by: markj (mentor)
Discussed with: kib
Differential Revision: https://reviews.freebsd.org/D20893
after the one where the possible block allocation begins, and allocate
a larger number of blocks than the current limit. This does not affect
the limit on minimum allocation size, which still cannot exceed
BLIST_MAX_ALLOC.
Use this change to modify swp_pager_getswapspace and its callers, so
that they can allocate more than BLIST_MAX_ALLOC blocks if they are
available.
Tested by: pho
Approved by: markj (mentor)
Differential Revision: https://reviews.freebsd.org/D20579
the allocation request, so that the blocks allocated are from the next
set of free blocks big enough to satisfy the minimum requirements of
the request, and the number of blocks allocated are as many as
possible, up to the specified maximum. The implementation of
swp_pager_getswapspace uses this parameter to ask for a number of
blocks between the new halved request size and the previous failed
request size. Thus a request for 32 blocks may fail, but instead of
getting only 16 blocks instead, the caller asks for 16 to 31 next, and
might get 19 or 27, which is closer to what they originally wanted.
I expect this to lead to bigger block allocations and less block
fragmentation, at least in some cases.
Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20001
change the binary search so that it does not depend on a single bit
only being set in the bitmask. Use bitpos more generally, and avoid
some clearing of bits to accommodate its current behavior.
Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20237
change the binary search so that it does not depend on a single bit
only being set in the bitmask. Use bitpos more generally, and avoid
some clearing of bits to accommodate its current behavior.
Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20232
the same thing, but is commented so that it might be better
understood.
Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20231
and the next one, and if blocks are allocated from the next leaf, it
walks back toward where it started, as long as there are interleaving
meta-nodes to be updated on account of the last free blocks under
those meta-nodes being allocated. Only if the walk goes all the way
back to the starting point must we calculate the position of the
meta-node that is the least-comment parent of one leaf and the next,
and update a bit in that meta-node to indicate the allocation of its
last free block.
There's no need to start calculating the position of that least-common
parent until the walk back reaches the original starting point, and
there's no need for a calculation that updates 'radius' to tell us
when we've walked back to the beginning, since comparing scan to next
suffices for that.
Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20229
resume where the last search left off. Suppose that there are no free
blocks of size 32, but plenty of size 16. If we repeatedly request
size 32 blocks, fail, and retry with size 16 blocks, then the failures
all reset the cursor to the beginning of memory, making the 16 block
allocation use a first fit, rather than next fit, strategy.
This change has blist_alloc make a copy of the cursor for its own
decision making, and only updates the real blist cursor after a
successful allocation, making those 16 block searches behave like
next-fit searches.
Approved by: markj (mentor)
Differential Revision: https://reviews.freebsd.org/D20177
and includes the last block represented by the leaf. The reasoning is that,
if the last block is included, then there must be no solution before that
one in the leaf, so the leaf cannot provide an allocation that big again;
indeed, the leaf cannot provide a solution bigger than range1.
Which is all correct, except that if the value of blk passed in did not
represent the first block of the leaf, because the cursor was pointing to
the middle of the leaf, then a possible solution before the cursor may have
been ignored, and bighint cannot be updated.
Consider the sequence allocate 63 (returning address 0), free 0,63 (freeing
that same block, and allocate 1 (returning 63). The result is that one
block is allocated from the first leaf, and the value of bighint is 0, so
that nothing can be allocated from that leaf until the only block allocated
from that leaf is freed. This change detects that skipped-over solution,
and when there is one it makes sure that the value of bighint is not changed
when the last block is allocated.
Submitted by: Doug Moore <dougm@rice.edu>
Tested by: pho
X-MFC with: r340402
Differential Revision: https://reviews.freebsd.org/D18474
cursor == 0.
Every call to blst_meta_alloc but the one at the root is made only when the
meta-node is known to include a free block, so that either the allocation
will succeed, the node hint will be updated, or the last block of the meta-
node range is, and remains, free. But the call at the root is made without
checking that there is a free block, so in the case that every block is
allocated, there is no hint update to prevent the current code from looping
forever.
Submitted by: Doug Moore <dougm@rice.edu>
Reported by: pho
Reviewed by: pho
Tested by: pho
X-MFC with: r340402
Differential Revision: https://reviews.freebsd.org/D17999
cursor lies in the middle of the space that the meta node represents, then
blanking the low bits of mask may make it zero, and break later code that
expects a nonzero value. Add a test that returns failure if the mask has
been cleared.
Submitted by: Doug Moore <dougm@rice.edu>
Reported by: pho
Tested by: pho
X-MFC with: r340402
Differential Revision: https://reviews.freebsd.org/D18058
Remove restrictions that prevent allocation requests to cross the
boundary between two meta nodes.
Replace the bmu_avail field in meta nodes with a bitmap that identifies
which subtrees have some free memory, and iterate over the nonempty
subtrees only in blst_meta_alloc. If free memory is scarce, this should
make searching for it faster.
Put the code for handling the next-leaf allocation in a separate
function. When taking blocks from the next leaf empties the leaf, be
sure to clear the appropriate bit in its parent, and so on, up to the
least-common ancestor of this leaf and the next.
Eliminate special terminator nodes, and rely instead on the fact that
there is a 0-bit at the end of the bitmask at the root of the tree that
will stop a meta_alloc search, or a next-leaf search, before the search
falls off the end of the tree. Make sure that the tree is big enough to
have space for that 0-bit.
Eliminate special all-free indicators. Lazy initialization of subtrees
stands in the way of having an allocation span a meta-node boundary, so
a subtree of all free blocks is not treated specially. Subtrees of
all-allocated blocks are still recognized by looking at the bitmask at
the root and finding 0.
Don't print all-allocated subtrees. Do print the bitmasks for meta
nodes, when tree-printing.
Submitted by: Doug Moore <dougm@rice.edu>
Reviewed by: alc
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D12635
We will have last_block < blocks if the block count is divisible
by BLIST_BMAP_RADIX, but a terminator node is still needed if the
tree isn't balanced. In this case we were overruning the blist
array by 16 bytes during initialization.
While here, add a check for the invalid blocks == 0 case.
PR: 231116
Reviewed by: alc, kib (previous version), Doug Moore <dougm@rice.edu>
Approved by: re (gjb)
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D17020
Mainly focus on files that use BSD 3-Clause license.
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.
appearing only where the code explicitly set it, but since much of the
data was not initialized, '-1' appeared other places too, and led to
panics. Clear the allocated data before initializing nonzero values by
allocating with M_ZERO.
Submitted by: Doug Moore <dougm@rice.edu>
Reported by: Oleg V. Nauman <oleg@theweb.org.ua>, cy
Tested by: Oleg V. Nauman <oleg@theweb.org.ua>
MFC after: 1 week
X-MFC with: r324420
Differential Revision: https://reviews.freebsd.org/D12627
nodes to allocate for the blist, and to initialize them. The computation
can be done much more quickly by identifying the terminating node, if any,
at every level of the tree and then summing the number of nodes at each
level that precedes the topmost terminator. The initialization can also be
done quickly, since settings at the root mark the tree as all-allocated, and
only a few terminator nodes need to be marked in the rest of the tree.
Eliminate blst_radix_init, and perform its two functions more simply in
blist_create.
The allocation of the blist takes places in two pieces, but there's no good
reason to do so, when a single allocation is sufficient, and simpler.
Allocate the blist struct, and the array of nodes associated with it, with a
single allocation.
Submitted by: Doug Moore <dougm@rice.edu>
Reviewed by: markj (an earlier version)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D11968
Modify blst_leaf_alloc to find allocations that cross the boundary between
one leaf node and the next when those two leaves descend from the same
meta node.
Update the hint field for leaves so that it represents a bound on how
large an allocation can begin in that leaf, where it currently represents
a bound on how large an allocation can be found within the boundaries of
the leaf.
The first phase of blst_leaf_alloc currently shrinks sequences of
consecutive 1-bits in mask until each has been shrunken by count-1 bits,
so that any bits remaining show where an allocation can begin, or until
all the bits have disappeared, in which case the allocation fails. This
change amends that so that the high-order bit is copied, as if, when the
last block was free, it was followed by an endless stream of free
blocks. It also amends the early stopping condition, so that the shrinking
of 1-sequences stops early when there are none, or there is only one
unbounded one remaining.
The search for the first set bit is unchanged, and the code path
thereafter is mostly unchanged unless the first set bit is in a position
that makes some of those copied sign bits matter. In that case, we look
for a next leaf, and at what blocks it can provide, to see if a
cross-boundary allocation is possible.
The hint is updated on a successful allocation that clears the last bit,
but it not updated on a failed allocation that leaves the last bit
set. So, as long as the last block is free, the hint value for the leaf is
large. As long as the last block is free, and there's a next leaf, a large
allocation can begin here, perhaps. A stricter rule than this would mean
that allocations and frees in one leaf could require hint updates to the
preceding leaf, and this change seeks to leave the freeing code
unmodified.
Define BLIST_BMAP_MASK, and use it for bit masking in blst_leaf_free and
blist_leaf_fill, as well as in blst_leaf_alloc.
Correct a panic message in blst_leaf_free.
Submitted by: Doug Moore <dougm@rice.edu>
Reviewed by: markj (an earlier version)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D11819
for analyzing the radix tree structures and reporting on the number, and
sizes, of maximal intervals of free blocks. The report includes the number
of maximal intervals, and also the number of them in each of several size
ranges, from small (size 1, or 3 to 4) to large (28657 to 46367) with size
boundaries defined by Fibonacci numbers. The report is written in the test
tool with the 's' command, or in a running kernel by sysctl.
The analysis of the radix tree frequently computes the position of the lone
bit set in a u_daddr_t, a computation that also appears in leaf allocation.
That computation has been moved into a function of its own, and optimized
for cases where an inlined machine instruction can replace the usual binary
search.
Submitted by: Doug Moore <dougm@rice.edu>
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D11906
removal of the "blk" parameter from blst_meta_alloc() had the unintended
effect of generating an out-of-range allocation when the cursor reaches
the end of the tree if the number of managed blocks in the tree equals
the so-called "radix" (which in the blist code is not the standard notion
of what a radix is but rather the maximum number of leaves in a tree of
the current height.) In other words, only certain swap configurations
were affected, which is why earlier testing did not reveal the problem.
Submitted by: Doug Moore <dougm@rice.edu>
Reported by: pho, kib
Tested by: pho
X-MFC with: r322459
Differential Revision: https://reviews.freebsd.org/D12106
another parameter that identifies a starting point in the memory address
block. Radix is a power of two, blk is a multiple of radix, and the
starting point is in the range [blk, blk+radix), so that blk can always be
computed from the other two. This change drops the blk parameter from the
meta functions and computes it instead. (On amd64, for example, this
change reduces subr_blist.o's text size by 7%.)
It also makes the radix parameters unsigned to address concerns that the
calculation of '-radix' might overflow without the -fwrapv option. (See
https://reviews.freebsd.org/D11819.)
Submitted by: Doug Moore <dougm@rice.edu>
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D11964
'skip', which denote, respectively, the largest number of blocks that can be
managed by a subtree of that height, and one less than the number of nodes
in a subtree of that height. This change removes the 'skip' argument from
those functions because 'skip' can be trivially computed from 'radius'.
This change also redefines 'skip' so that it denotes the number of nodes in
the subtree, and so changes loop upper bound tests from '<= skip' to '<
skip' to account for the change.
The 'skip' field is also removed from the blist struct.
The self-test program is changed so that the print command includes the
cursor value in the output.
Submitted by: Doug Moore <dougm@rice.edu>
MFC after: 1 week
"leaf" functions for alloc, free, and fill. After the change, the interface
functions call "meta" unconditionally, and the "meta" functions recur
unconditionally in looping over their descendants. The "meta" functions
start with a validity test, and then a test for the "leaf" case, before
falling into the general recursive case. This simplifies and shrinks the
code, and, for "free" and "fill" moves panic tests that check the same meta
node repeatedly in a loop to a place that will have each node tested once.
Remove irrelevant null checks from blist_free and blist_fill.
Make the code that initializes a meta node the same in blist_meta_alloc and
blist_meta_fill.
Parenthesize return expressions in blst_meta_fill.
Submitted by: Doug Moore <dougm@rice.edu>
MFC after: 1 week
of-line whitespace, remove excessive whitespace and blank lines, remove
dead code, follow our standard style for function definitions, and
correct grammatical and factual errors in some of the comments.
Submitted by: Doug Moore <dougm@rice.edu>
MFC after: 1 week
performance.
To find in the leaf bitmap all ranges of sufficient length, use a doubling
strategy with shift-and-and until each bit still set represents a bit
sequence of length 'count', or until the bitmask is zero. In the latter
case, update the hint based on the first bit sequence length not found to
be available. For example, seeking an interval of length 12, the set bits
of the bitmap would represent intervals of length 1, then 2, then 3, then
6, then 12. If no bits are set at the point when each bit represents an
interval of length 6, then the hint can be updated to 5 and the search
terminated.
If long-enough intervals are found, discard those before the cursor. If
any remain, use binary search to find the position of the first of them,
and allocate that interval.
Submitted by: Doug Moore <dougm@rice.edu>
Reviewed by: kib, markj
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D11426
and "next_skip" variables. The "skip" value in struct blist has long been
a 64-bit quantity but various functions have implicitly truncated this
value to 32 bits. Now, all arithmetic involving the "skip" value is 64
bits wide. (This should allow us to relax the size limit on a swap device
in the swap pager.)
Maintain the ability to test this allocator as a user-space application by
including <stdbool.h>.
Remove an unused variable from blst_radix_print().
Reviewed by: kib, markj
MFC after: 4 weeks
Differential Revision: https://reviews.freebsd.org/D11358
that disk writes are more likely to be sequential. This change is
beneficial on both the solid state and mechanical disks that I've
tested. (A similar change in allocation policy was made by DragonFly
BSD in 2013 to speed up Poudriere with "stressful memory parameters".)
Increase the width of blst_meta_alloc()'s parameter "skip" and the local
variables whose values are derived from it to 64 bits. (This matches the
width of the field "skip" that is stored in the structure "blist" and
passed to blst_meta_alloc().)
Eliminate a pointless check for a NULL blist_t.
Simplify blst_meta_alloc()'s handling of the ALL-FREE case.
Address nearby style errors.
Reviewed by: kib, markj
MFC after: 5 weeks
Differential Revision: https://reviews.freebsd.org/D11247
additional allocation overhead. Previously, blst_meta_alloc() updated the
hint after every successful allocation. However, these "eager" hint
updates are of no actual benefit if, instead, the "lazy" hint update at
the start of blst_meta_alloc() is generalized to handle all cases where
the number of available blocks is less than the requested allocation.
Previously, the lazy hint update at the start of blst_meta_alloc() only
handled the ALL-FULL case. (I would also note that this change provides
consistency between blist_alloc() and blist_fill() in that their hint
maintenance is now entirely lazy.)
Eliminate unnecessary checks for terminators in blst_meta_alloc() and
blst_meta_fill() when handling ALL-FREE meta nodes.
Eliminate the field "bl_free" from struct blist. It is redundant. Unless
the entire radix tree is a single leaf, the count of free blocks is stored
in the root node. Instead, provide a function blist_avail() for obtaining
the number of free blocks.
In blst_meta_alloc(), perform a sanity check on the allocation once rather
than repeating it in a loop over the meta node's children.
In blst_leaf_fill(), use the optimized bitcount*() function instead of a
loop to count the blocks being allocated.
Add or improve several comments.
Address some nearby style errors.
Reviewed by: kib
MFC after: 6 weeks
Differential Revision: https://reviews.freebsd.org/D11146
what this field represented was also inaccurate.) Suggested by: kib
In r178792, blist_create() grew a malloc flag, allowing M_NOWAIT to be
specified. However, blist_create() was not modified to handle the
possibility that a malloc() call failed. Address this omission.
Increase the width of the local variable "radix" to 64 bits. (This
matches the width of the corresponding field in struct blist.)
Reviewed by: kib
MFC after: 6 weeks
quantity as the size of the range to fill, but returns a 32-bit quantity
as the number of blocks that were allocated to fill that range. This
revision corrects that mismatch. Currently, swaponsomething() limits
the size of a swap area to prevent arithmetic arithmetic overflow in
other parts of the blist allocator. That limit has also prevented this
type mismatch from causing problems.
Reviewed by: kib, markj
MFC after: 6 weeks
Differential Revision: https://reviews.freebsd.org/D11096
subtree is already zero, then setting the "largest contiguous free block"
hint for that subtree to anything other than zero makes no sense. To be
clear, assigning a value to the hint that is too large is not a correctness
problem, only a pessimization.
Dragonfly BSD has applied the same change to blst_meta_alloc() but not
blst_meta_fill().
MFC after: 6 weeks
testing purposes. However, over the years, various changes to the kernel
have broken this feature. This revision applies some fixes to get user-
space compilation working again. There are no changes in this revision
to code that is used by the kernel.
MFC after: 3 days
pager used a different scheme for striping the allocation of swap space
across multiple devices. And, although blist_fill() was intended to support
fill operations with large counts, the old striping scheme never performed a
fill larger than the stripe size. Consequently, the misplacement of a
sanity check in blst_meta_fill() went undetected. Now, moving forward in
time to r118390, a new scheme for striping was introduced that maintained a
blist allocator per device, but as noted in r318995, swapoff_one() was not
fully and correctly converted to the new scheme. This change completes what
was started in r318995 by fixing the underlying bug in blst_meta_fill() that
stops swapoff_one() from simply performing a single blist_fill() operation.
Reviewed by: kib
MFC after: 5 days
Differential Revision: https://reviews.freebsd.org/D11043
short, half of the memory that is allocated to implement the radix tree is
wasted because we did not change "u_daddr_t" to be a 64-bit unsigned int
when we changed "daddr_t" to be a 64-bit (signed) int. (See r96849 and
r96851.)
Reviewed by: kib, markj
Tested by: pho
MFC after: 5 days
Differential Revision: https://reviews.freebsd.org/D11028
