x/tools/gopls: high memory consumption in certain workspaces when staticcheck is enabled

[findleyr]

Forked from #45457 (comment), where @folago is reporting that they still encounter high memory consumption in their workspace. In fact, this memory consumption is even higher than gopls@v0.11.0.

I suspect analysis facts, the import graph for open packages, or perhaps a memory leak. Unfortunately this reproducer is not open source, but with some help we should be able to narrow down the cause.

CC @adonovan

[findleyr]

Per ongoing discussion in #45457, we have narrowed this down to SSA/SSI analyzers that are enabled (nilness and staticcheck).

Looking at the profile posted there, it appears that encoding/decoding staticcheck's IR is causing quite a bit of allocation:

(pprof) top
Showing nodes accounting for 13800.10MB, 88.23% of 15640.41MB total
Dropped 449 nodes (cum <= 78.20MB)
Showing top 10 nodes out of 105
      flat  flat%   sum%        cum   cum%
 9905.08MB 63.33% 63.33% 10184.11MB 65.11%  honnef.co/go/tools/go/ir.memberFromObject
 1119.06MB  7.15% 70.48%  1392.08MB  8.90%  golang.org/x/tools/go/types/objectpath.namedMethods
  541.59MB  3.46% 73.95%  2420.59MB 15.48%  golang.org/x/tools/internal/facts.(*Decoder).Decode
  522.31MB  3.34% 77.29%   522.31MB  3.34%  os.ReadFile
  351.41MB  2.25% 79.53%   351.41MB  2.25%  reflect.unsafe_NewArray
  325.03MB  2.08% 81.61%   325.03MB  2.08%  honnef.co/go/tools/go/ir.NewConst (inline)
  310.03MB  1.98% 83.59%   310.03MB  1.98%  go/types.NewParam (inline)
  268.52MB  1.72% 85.31%   268.52MB  1.72%  go/types.Id
  241.51MB  1.54% 86.86%   241.51MB  1.54%  encoding/gob.decString
  215.56MB  1.38% 88.23%   719.62MB  4.60%  honnef.co/go/tools/go/ir.makeWrapper

As reported by @folago, with staticcheck/nilness enabled they are observing up to 12GB of disk reads, vs ~300MB of reads without. This indicates that SSA structures may be consuming more than the fixed 1GB of cache, which could result in a lot of churn.

Next step: try to reproduce this in an open source repository that we know to have expensive analysis, such as hashicorp/terraform-provider-aws.

(I'll note that I am intentionally not CCing Dominik yet, as I suspect our driver lacks some sophistication, and don't want to bother him :) )

[findleyr]

This repro'ed on hashicorp/terraform-provider-aws: just open the internal/provider package (or anything that imports it).

@adonovan and I investigated, and thus far, we don't see anything "wrong" (apart from the process consuming all available memory and crashing, of course). Building the staticcheck IR is expensive, and now that gopls has proper fact support, the staticcheck buildir analyzer must be run on everything in the forward transitive closure of open packages. When that closure is large, it take a long time. I'll note that the nilness analyzer and buildssa analyzers don't use facts, so unlike buildir it is NOT the case that buildssa must be run on all dependencies. That's why enabling nilness was not nearly as expensive as staticcheck.

I'll note that running staticcheck on internal/provider also takes a while. However, staticcheck does a better job of limiting the high water mark for memory usage: on my computer it tops out at 10GB and doesn't go much higher.

Therefore, I think there are three action items:

• Limit analysis concurrency to reduce the high water mark of memory consumed by analysis in gopls.
• Check with @dominikh whether this performance is consistent with his expectations.
• (possibly) separate "fast" and "slow" analyzers, so that we may prioritize running fast analyzers with low latency.

[dominikh]

staticcheck using 10 GB seems quite high to me. I'll try and do some analysis tomorrow.

[findleyr]

Thanks @dominikh. I'll just note that this repository was chosen because it is known to be very expensive to analyze. It has some large low-level packages. 10GB does not seem entirely unreasonable. But it may be worthwhile to understand the cost a bit better: e.g. is there some common edge through a method that causes buildir to be effectively quadratic?

[gopherbot]

Change https://go.dev/cl/511215 mentions this issue: gopls/internal/lsp/cache: UX improvements for analysis

[gopherbot]

Change https://go.dev/cl/511216 mentions this issue: go/types/objectpath: avoid sorting methods for gopls

[adonovan]

The problem is very easy to reproduce without staticcheck or buildir, and without gopls.

Simply add a dummy fact to nilness.Analyzer.FactTypes and run the nilness command:

terraform-provider-aws$ (cd ~/w/xtools && go build -o nilness ) && time ~/w/xtools/nilness -cpuprofile=prof ./internal/provider/
... time passes, memory fades ...

See #61506.