Use RTS --disable-delayed-os-memory-return by default for the node #2493
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By default on Linux the RTS uses a fast method of returning memory to the kernel. This fast method allows the kernel to free the memory lazily when there is memory pressure. The downside of leting the kernel do it lazily is that the RSS measure is also only updated lazily. This has the effect of scaring system admins that the RSS is really high, when in reality that does not reflect the actual amount of memory being used. So by using +RTS --disable-delayed-os-memory-return we ask the RTS to not use the faster freeing method and use the normal method that updates the RSS eagerly.
dcoutts
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2493: Use RTS --disable-delayed-os-memory-return by default for the node r=nc6 a=dcoutts By default on Linux the RTS uses a fast method of returning memory to the kernel. This fast method allows the kernel to free the memory lazily when there is memory pressure. The downside of leting the kernel do it lazily is that the RSS measure is also only updated lazily. This has the effect of scaring system admins that the RSS is really high, when in reality that does not reflect the actual amount of memory being used. So by using +RTS --disable-delayed-os-memory-return we ask the RTS to not use the faster freeing method and use the normal method that updates the RSS eagerly. Co-authored-by: Duncan Coutts <duncan@well-typed.com>
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For some reason this is failing on I pushed a commit to limit the use of this RTS option to |
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@newhoggy Can you approve? Seems like it needs a codeowner |
dcoutts
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Mar 16, 2021
| else | ||
| ghc-options: "-with-rtsopts=-T -I0 -N2 -A16m --disable-delayed-os-memory-return" | ||
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| if impl(ghc >= 8.10) |
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But look at what that does. This mean we use no args at all for earlier ghc versions.
I think it might actually work to use multiple -with-rtsopts like:
ghc-options: "-with-rtsopts=-T -I0 -N1 -A16m"
if arch(arm)
ghc-options: "-with-rtsopts=-N1"
else
ghc-options: "-with-rtsopts=-N2"
if impl(ghc >= 8.10)
ghc-options: "-with-rtsopts=--disable-delayed-os-memory-return"
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BTW, no need to test this in CI, check in any local "hello world" local Haskell program that it works to use multiple -with-rtsopts= and that they get combined.
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By default on Linux the RTS uses a fast method of returning memory to
the kernel. This fast method allows the kernel to free the memory
lazily when there is memory pressure. The downside of leting the kernel
do it lazily is that the RSS measure is also only updated lazily.
This has the effect of scaring system admins that the RSS is really
high, when in reality that does not reflect the actual amount of memory
being used.
So by using +RTS --disable-delayed-os-memory-return we ask the RTS to
not use the faster freeing method and use the normal method that updates
the RSS eagerly.