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Mmap fix on system with 64k pagesize. #59695

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Mmap fix on system with 64k pagesize. #59695

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bee04ae
Update runtests.jl
green-br Sep 30, 2025
dd7f328
Update Mmap.jl
green-br Sep 30, 2025
5e82dc1
Update sysinfo.jl
green-br Oct 1, 2025
e878c25
Update sysinfo.jl
green-br Oct 1, 2025
28b9a5b
Update Mmap.jl
green-br Oct 1, 2025
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2 changes: 1 addition & 1 deletion stdlib/Mmap/src/Mmap.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@ import Base: OS_HANDLE, INVALID_OS_HANDLE

export mmap

const PAGESIZE = Int(Sys.isunix() ? ccall(:jl_getpagesize, Clong, ()) : ccall(:jl_getallocationgranularity, Clong, ()))
PAGESIZE = Int(Sys.isunix() ? ccall(:jl_getpagesize, Clong, ()) : ccall(:jl_getallocationgranularity, Clong, ()))
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@vtjnash is

Suggested change
PAGESIZE = Int(Sys.isunix() ? ccall(:jl_getpagesize, Clong, ()) : ccall(:jl_getallocationgranularity, Clong, ()))
const PAGESIZE = OncePerProcess{Int}() do
Int(Sys.isunix() ? ccall(:jl_getpagesize, Clong, ()) : ccall(:jl_getallocationgranularity, Clong, ()))
end

the right way to do this on master?

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But then all references to PAGESIZE should be changed to PAGESIZE(). Apparently there are some packages which were using this internal symbol assuming it was a constant, and we'll need to update them: https://juliahub.com/ui/Search?type=code&q=Mmap.PAGESIZE

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I'm not certain you need the overhead of OncePerProcess to memoize the read of the getpagesize variable

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So this should just be a regular function?

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I opened #59712 as an alternative to this PR, to create a pagesize function.

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Thanks for taking a look - I was looking eleswhere in the code and the Sys module which seems to use __init__ function to set similar type of variables. e.g. Sys module

Made me think whether PAGESIZE should be in Sys to keep these sorts of settings in the same location.

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Agreed, Sys.__init__ makes sense, then just needs using Sys: PAGESIZE here

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Attempted to test this out or at least draft it.


# for mmaps not backed by files
mutable struct Anonymous <: IO
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1 change: 1 addition & 0 deletions stdlib/Mmap/test/runtests.jl
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Expand Up @@ -268,6 +268,7 @@ A2 = mmap(s, Matrix{Int}, (m,n))
seek(s, 0)
A3 = mmap(s, Matrix{Int}, (m,n), convert(Int64, 2*sizeof(Int)))
@test A == A3
seek(s, 0)
A4 = mmap(s, Matrix{Int}, (m,150), convert(Int64, (2+150*m)*sizeof(Int)))
@test A[:, 151:end] == A4
close(s)
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