sync: add Pool type #4720
Labels
Comments
I would like this very much. In one project at CloudFlare I have implemented some code to recycle []byte buffers which are used to hold web pages. These were being allocated and released to the GC for cleanup. We now have a small package that accepts them back on a channel and maintains a list in a goroutine of available buffers. Anyone needing a buffer just receives on a channel and gets the next item from the list or a new buffer if none are available. The code also keeps track of the size of the list discarding buffers if it looks like there are 'too many'. The idea being that we don't keep buffers that were allocated during a burst of activity. |
What you are proposing is essentially to provide free() function. That's the easiest and
the most efficient way to implement your interface :)
Another option is to provide generic pool for interface{}:
type Pool struct {...}
func (p *Pool) Get() interface{}
func (p *Pool) Put(res interface{}) bool
func (p *Pool) Drain() []interface{}
func (p *Pool) SetCapacity(global, local int)
And then if the buffer sizes have some reasonable limits, then one can have, say, 16
pools for blocks of size 4k, 8k, 12k, ..., 64k, and manually choose the right one. Brad,
would it suffice dl.google.com server?
The idea behind SetCapacity(global, local int) is that you can set local=0, and then it
will be a slower pool for expensive resources.
Yes, the fast version with local cache would benefit greatly from per-m caches.
|
> And then if the buffer sizes have some reasonable limits, then one can have, > say, 16 pools for blocks of size 4k, 8k, 12k, ..., 64k, and manually choose > the right one. Brad, would it suffice dl.google.com server? I think asking for and freeing n bytes is common enough that it should be first-class. We shouldn't make people create their own set of ever size class []byte. |
The problem with runtime.Free is that using it incorrectly from buggy package A affects
not-buggy package B.
With my NewBytePool proposal as implemented for dl.google.com, the byte pools are owned
by whoever made them.
But for everything needing []byte that I care about right now (io Copy buffers, ioutil
Discard buffers, and dl.google.com buffers), they're all fixed size. So I'm fine
ignoring variably-sized []byte allocation pools and not muddling this discussion.
Pools of interface{} works for me.
|
This bug is about sync.Cache, a cache of interchangeable fixed-size items. The idea is that a sync.Cache might replace fmt's internal cache, and it might be used for a cache of fixed-size buffers for io.Copy. A cache of non-fixed-size items such as variable-length byte slices is quite a bit more complicated. |
I have a preliminary version of sync.Cache based on proc-local data: https://golang.org/cl/7686043/ And here it is applied to fmt: https://golang.org/cl/7637047 benchmark old ns/op new ns/op delta BenchmarkSprintfInt 363 368 +1.38% BenchmarkSprintfInt-2 457 249 -45.51% BenchmarkSprintfInt-4 850 142 -83.29% BenchmarkSprintfInt-8 1220 78 -93.61% BenchmarkSprintfInt-16 1226 58 -95.22% BenchmarkManyArgs 2233 2296 +2.82% BenchmarkManyArgs-2 1255 1316 +4.86% BenchmarkManyArgs-4 1250 714 -42.88% BenchmarkManyArgs-8 1100 429 -61.00% BenchmarkManyArgs-16 1528 361 -76.37% |
Pretty please? :) The runtime part looks relatively tiny: https://golang.org/cl/7686043/diff/6001/src/pkg/runtime/proc.c |
I'm concerned that sync.Cache is exported and will let a genie out of the bottle we will have to support for all of Go 1.x. What if, for Go 1.1, in only the fmt and net/http packages (or net/textproto), a copy of the sync.Cache was added, in a separate file, without exporting the type? Dave |
|
Comment 18 by tylor@torbit.com: Please call this construct a Pool (or FixedPool) rather than a Cache if it comes into existence. I can already imagine myself explaining to new people over and over again on #go-nuts that sync.Cache is actually a pool, etc etc... |
As a user of go to write backend services, this is the one feature I was truly looking forward to for 1.2. All the ad-hoc leaky buckets I'm making are nothing but boilerplate, and I've love to be able to use something like sync.Pool. Is premature optimization a problem? Yes, but for my services, stop-the-world GC pauses are worse, and I can't profile ahead of time for every combination of real world scenarios. The obvious places that need a pool will get them regardless. Please reconsider. A naive sync.Pool helps me get products to production faster. A GC-aware sync.Pool would be a godsend. |
API proposal from Russ: https://groups.google.com/forum/#!searchin/golang-dev/gc-aware/golang-dev/kJ_R6vYVYHU/LjoGriFTYxMJ |
CL proposal: https://golang.org/cl/41860043/ |
|
This issue was updated by revision 8c6ef06. R=golang-dev, rsc, cshapiro, iant, r, dvyukov, khr CC=golang-dev https://golang.org/cl/41860043 |
|
This issue was updated by revision 0f93118. R=golang-dev, iant CC=golang-dev https://golang.org/cl/43990043 |
|
This issue was updated by revision 46b4ed2. R=golang-dev, iant CC=golang-dev https://golang.org/cl/37720047 |
|
This issue was updated by revision 93e4a9d. R=golang-dev, iant CC=golang-dev https://golang.org/cl/44080043 |
|
This issue was updated by revision b682f6d. R=golang-dev, rsc CC=golang-dev https://golang.org/cl/44150043 |
|
This issue was updated by revision 90e9669. R=golang-dev, rsc CC=golang-dev https://golang.org/cl/44150043 »»» TBR=golang-dev CC=golang-codereviews https://golang.org/cl/48190043 |
|
CL https://golang.org/cl/8202 mentions this issue. |
dr2chase
added a commit
that referenced
this issue
May 1, 2015
This includes the following information in the per-function summary:
outK = paramJ encoded in outK bits for paramJ
outK = *paramJ encoded in outK bits for paramJ
heap = paramJ EscHeap
heap = *paramJ EscContentEscapes
Note that (currently) if the address of a parameter is taken and
returned, necessarily a heap allocation occurred to contain that
reference, and the heap can never refer to stack, therefore the
parameter and everything downstream from it escapes to the heap.
The per-function summary information now has a tuneable number of bits
(2 is probably noticeably better than 1, 3 is likely overkill, but it
is now easy to check and the -m debugging output includes information
that allows you to figure out if more would be better.)
A new test was added to check pointer flow through struct-typed and
*struct-typed parameters and returns; some of these are sensitive to
the number of summary bits, and ought to yield better results with a
more competent escape analysis algorithm. Another new test checks
(some) correctness with array parameters, results, and operations.
The old analysis inferred a piece of plan9 runtime was non-escaping by
counteracting overconservative analysis with buggy analysis; with the
bug fixed, the result was too conservative (and it's not easy to fix
in this framework) so the source code was tweaked to get the desired
result. A test was added against the discovered bug.
The escape analysis was further improved splitting the "level" into
3 parts, one tracking the conventional "level" and the other two
computing the highest-level-suffix-from-copy, which is used to
generally model the cancelling effect of indirection applied to
address-of.
With the improved escape analysis enabled, it was necessary to
modify one of the runtime tests because it now attempts to allocate
too much on the (small, fixed-size) G0 (system) stack and this
failed the test.
Compiling src/std after touching src/runtime/*.go with -m logging
turned on shows 420 fewer heap allocation sites (10538 vs 10968).
Profiling allocations in src/html/template with
for i in {1..5} ;
do go tool 6g -memprofile=mastx.${i}.prof -memprofilerate=1 *.go;
go tool pprof -alloc_objects -text mastx.${i}.prof ;
done
showed a 15% reduction in allocations performed by the compiler.
Update #3753
Update #4720
Fixes #10466
Change-Id: I0fd97d5f5ac527b45f49e2218d158a6e89951432
Reviewed-on: https://go-review.googlesource.com/8202
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
This issue was closed.
Sign up for free
to subscribe to this conversation on GitHub.
Already have an account?
Sign in.
Many Go programs and packages try to reuse memory either for locality reasons or to reduce GC pressure: pkg/regexp: pool of available threads pkg/net/http: wants to reuse a lot and has TODOs, but has resisted the temptation so far pkg/fmt: print.go's var ppFree = newCache(func() interface{} { return new(pp) }) pkg/io: for the 32 KB copy buffers; see discussion at https://golang.org/cl/7206048/ (which spawned this bug). These buffers showed up in dl.google.com profiles. Lot of things in the Go standard library use io.Copy, so this can't be fixed by caller code. pkg/io/ioutil: see https://code.google.com/p/go/source/browse/src/pkg/io/ioutil/blackhole.go for reusing the Discard buffers dl.google.com: was allocating hundreds of MB/s, causing lots of GCs, until we added a google-internal (for now) []byte pool reuse library, with an API like: package pool func NewBytePool(...opts...) *BytePool func (*BytePool) Alloc(n int) []byte func (*BytePool) Free(buf []byte) There are two distinct but related uses: * reusing small-ish structs (like regexp, fmt) * reusing bigger []byte (io, ioutil, dl.google.com) The former would benefit more from a per-m cache. Dmitry and Russ had some thoughts towards this. With big []byte, per-m doesn't matter as much, but you do care about things not being able to burst to some threshold (yet not retain memory for too long unnecessarily) and grouping things into size classes (i.e. a "user-space" tcmalloc) when the sizes differ. The question: Do we make a new package or facility to promote this pattern? The status quo is that it keeps being reimplemented in each package privately, and poorly. It'd be nice to have a good implementation that everybody could reuse. Almost all uses are beyond what I believe are reasonable with static liveness/escape analysis. This isn't a GC problem, because by the time the GC's involved, it's too late and we've already allocated too much. This is about allocating less and reusing memory when caller code knows it's no longer needed.The text was updated successfully, but these errors were encountered: