zend: optimisation for zend_page_size for macos. #19494
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Using the kernel global vm_page_size set by the dynamic linker before the process starts.
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From what I see here, this seems to be accurate: https://github.com/apple/darwin-xnu/blob/2ff845c2e033bd0ff64b5b6aa6063a1f8f65aa32/osfmk/mach/arm/vm_param.h#L85
@devnexen Is there some public documentation rather than just code that this works?
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And does this result in a measurable improvement? |
That is the issue in general with macos, however in this case here sysconf to give you an idea then here getpagesize. So we save the whole syscall at first access basically. Normally, you would at least call getpagesize instead like with FreeBSD. |
Zend/zend.c
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| @@ -1275,6 +1279,10 @@ ZEND_API size_t zend_get_page_size(void) | |||
| SYSTEM_INFO system_info; | |||
| GetSystemInfo(&system_info); | |||
| return system_info.dwPageSize; | |||
| #elif defined(__APPLE__) | |||
| /* Is in fact the global vm_page_size which is a kernel global | |||
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If the purpose is to safe syscall, wouldn't it be better to cache the result like in https://github.com/apple-open-source-mirror/Libc/blob/5e566be7a7047360adfb35ffc44c6a019a854bea/gen/FreeBSD/getpagesize.c#L50-L64 for all platforms?
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Some of the callsites already cache it., like here. If you mean in here to me windodws/posix cases would benefit it, for mac it is just a variable.
That does not seem particularly worth it going into undocumented territory? |
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fair enough. with Mac it is often like this, someone figure something out and we share amongst oss projects :) Anyhow, would calling getpagesize like for FreeBSD case suit you ? |
Zend/zend.c
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| /* This returns the value obtained from | ||
| * the auxv vector, avoiding a syscall. */ |
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Is this comment accurate for macOS? From your link https://github.com/apple-open-source-mirror/Libc/blob/5e566be7a7047360adfb35ffc44c6a019a854bea/gen/FreeBSD/sysconf.c#L296 it appears that sysconf(_SC_PAGESIZE) just calls getpagesize(), so we only save a single function call, not a syscall, no?
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yes I can correct the comment.
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Using the getpagesize() call instead which saves one call.
Using the kernel global vm_page_size set by the dynamic linker before the process starts.