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Re: the page size bug

From: Mike Gran
Subject: Re: the page size bug
Date: Wed, 8 Mar 2017 21:32:05 +0000 (UTC)

On Wednesday, March 8, 2017 12:42 PM, Andy Wingo <address@hidden> wrote:

> The problem with the malloc path is that not only is it a bit slower, as
> it has to page in data that might not be needed, it doesn't share memory
> between processes.  So if the system supports mmap, Guile will use mmap
> to load its ELF images (.go files).

In trying to get Guile to work on Cygwin, I've reverted to the
malloc path by #undef'ing HAVE_SYS_MMAN_H.  The mmap path is broken,
as you note.

> One solution to this issue would be to choose target-specific page
> sizes.  This is still a little tricky; on amd64 for example, systems
> commonly have 4KB pages, but they are allowed by the ABI to have any
> multiple-of-2 page size up to 64 KB.  On Cygwin, pages are 4kB but they
> can only be allocated 16 at a time.  MIPS and ARM64 can use 64K pages
> too and that's not uncommon.

Cygwin wants its users to not second-guess the 64k pagesize it
provides as its interface.  It sees the 16x 4k pagesize as an internal
detail that it is trying to abstract away.

Mike Gran

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