[NativeAOT] Support variable page size on Linux Arm64 #88710

VSadov · 2023-07-12T00:22:18Z

OS Page size can be configured on some platforms. (i.e. Linux arm64)

ghost · 2023-07-12T00:22:34Z

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Issue Details

OS Page size can be configured on some platforms. (i.e. Linux arm64)

Fixes: #75737

Author:	VSadov
Assignees:	-
Labels:	`area-NativeAOT-coreclr`
Milestone:	-

jkotas · 2023-07-12T06:21:02Z

src/coreclr/nativeaot/Runtime/ThunksMapping.cpp

@@ -56,7 +57,7 @@ void EncodeThumb2Mov32(uint16_t * pCode, uint32_t value, uint8_t rDestination)

 COOP_PINVOKE_HELPER(int, RhpGetNumThunkBlocksPerMapping, ())
 {
-    static_assert((THUNKS_MAP_SIZE % OS_PAGE_SIZE) == 0, "Thunks map size should be in multiples of pages");
+    ASSERT_MSG((THUNKS_MAP_SIZE % OS_PAGE_SIZE) == 0, "Thunks map size should be in multiples of pages");


IIRC, 64kB is a common page size on Linux Arm64. It is going to assert there.

Ask @janvorli if you need help getting Linux arm64 machine configured like that for testing.

with #define THUNKS_MAP_SIZE (max(0x8000, OS_PAGE_SIZE)) would it assert?

It would still be interesting to run this on an actual system with 64K pages.

You are right. I got it backwards.

jkotas · 2023-07-12T06:24:20Z

src/coreclr/nativeaot/Runtime/unix/PalRedhawkInline.h

+FORCEINLINE int32_t PalOsPageSize()
+{
+#ifdef HOST_APPLE
+    return 0x4000;


This is true for arm64. Is it true on x64 machines as well? Or are we pessimizing it here for simplicity?

Is it true on x64 machines as well?

No, it is not. macOS x64 still uses 4Kb pages.

I forgot that OSX on x64 is still possible :-). Yes, on x64 everything uses 4K as OS page size.

Is it the case even with x86 emulator on OSX arm64?

The OS can emulate larger page size than the hardware supports, but doing it the other way around is hard.

Is it the case even with x86 emulator on OSX arm64?

good question. arm64 should support 4K pages. However, what Rosetta does when running on M1 - not sure. I'd guess 16K pages on x64 could be a breaking change. There is one way to find out.

Is it the case even with x86 emulator on OSX arm64?

Yes, is it (with the exception of the first ARM Dev Kits that are no longer in circulation).

Yes, is it (with the exception of the first ARM Dev Kits that are no longer in circulation).

I assume that is the "yes" for 4K pages? :-)

I wonder if there are any docs, but emulation could be too much of a corner case and a temporary solution, to document such details.

Yes, always 4K pages even in Rosetta emulation.

jkotas · 2023-07-12T06:29:55Z

src/coreclr/nativeaot/Runtime/unix/PalRedhawkUnix.cpp

+    if (saved_pagesize)
+        return saved_pagesize;
+
+    // Prefer sysconf () as it's signal safe.


Do we care about signal safety here? If we do, we can initialize this during PalInit like it is done in CoreCLR.

The same pattern is used in mono in multiple paces. I've just copied it, together with the comment. I guess when either one can be used signal safety might be an advantage.
We do not call this from code that must be signal-safe right now.

I think we can drop the comment about signal safety - not very relevant to us, but keep the pattern - use sysconf, if can, then use getpagesize.

jkotas · 2023-07-12T06:31:08Z

src/coreclr/nativeaot/Runtime/unix/PalRedhawkUnix.cpp

+#if defined (HAVE_SYSCONF) && defined (_SC_PAGESIZE)
+    saved_pagesize = sysconf(_SC_PAGESIZE);
+#else
+    saved_pagesize = getpagesize();


I have notice that CoreCLR PAL uses getpagesize, but GC uses sysconf(_SC_PAGESIZE). Is there difference between the two? Which one is better?

the documentation seems to direct to sysconf as more portable:

DESCRIPTION The function getpagesize() returns the number of bytes in a memory page, where "page" is a fixed-length block, the unit for memory allocation and file mapping performed by mmap(2). CONFORMING TO SVr4, 4.4BSD, SUSv2. In SUSv2 the getpagesize() call is labeled LEGACY, and in POSIX.1-2001 it has been dropped; HP-UX does not have this call. NOTES Portable applications should employ sysconf(_SC_PAGESIZE) instead of getpagesize():

So just call sysconf(_SC_PAGESIZE) everywhere without any ifdefs?

I thought so, but mono does ifdefs and has a fallback to getpagesize. Perhaps the call is not always present. I noticed that coreclr also uses sysconf conditionally. Maybe to handle some legacy cases where it is not there or for some other platforms.

My conclusion was - we can see one or another missing. If both are present, use sysconf. If neither - fail to build.

From the mono pattern it looks like it is also possible that sysconf is there, but _SC_PAGESIZE is missing.

Is there sysconf on bionic or on some FreeBSD derived OS for consoles?
I think from portability point of view the pattern from mono has some advantages, while not a big burden on mainstream Linux.

GC calls sysconf unconditionally and it works fine for all platforms that we care about.

I would expect that this ifdef is only needed for some old systems that we do not care about.

no point to be more portable than GC. I will switch to calling sysconf unconditionally then.

src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ThunkPool.cs

Co-authored-by: Filip Navara <filip.navara@gmail.com>

jkotas

Thank you!

am11 · 2023-07-14T14:37:22Z

src/coreclr/nativeaot/Runtime/unix/PalRedhawkUnix.cpp

+
+void InitializeOsPageSize()
+{
+    g_RhPageSize = (uint32_t)sysconf(_SC_PAGE_SIZE);


Perhaps better:

#ifdef OS_PAGE_SIZE g_RhPageSize = (uint32_t)OS_PAGE_SIZE; #else g_RhPageSize = (uint32_t)sysconf(_SC_PAGE_SIZE); #endif

, delete PalOsPageSize and use PalGetOsPageSize everywhere?

nit: Os -> OS (two-letter abbreviation rule)

delete PalOsPageSize and use PalGetOsPageSize everywhere?

I think we need one that inlines, and one that does not. (and one calls another, if needed)
I did not replace uses of OS_PAGE_SIZE, though, as that would be a lot of changes and keeping OS_PAGE_SIZE would match closer the similar pattern in GC code.

VSadov added 4 commits July 11, 2023 13:56

stack probe

8aee074

probe size on x86

cae77f8

OS_PAGE_SIZE

f5b5928

getpagesize

af0ffbe

VSadov requested a review from MichalStrehovsky as a code owner July 12, 2023 00:22

dotnet-issue-labeler bot added the area-NativeAOT-coreclr label Jul 12, 2023

ghost assigned VSadov Jul 12, 2023

make GCC happy

495f851

jkotas reviewed Jul 12, 2023

View reviewed changes

VSadov added 2 commits July 12, 2023 09:40

call sysconf(_SC_PAGESIZE) unconditionally

4357ab0

initialize OS page in PalInit

f92b118

VSadov force-pushed the pgSize branch from 71b20f9 to f92b118 Compare July 12, 2023 18:07

filipnavara approved these changes Jul 12, 2023

View reviewed changes

src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ThunkPool.cs Outdated Show resolved Hide resolved

PR feedback

437df5b

Co-authored-by: Filip Navara <filip.navara@gmail.com>

This was referenced Jul 12, 2023

Timeout in Microsoft.Gen.OptionsValidation.Unit.Test.EmitterTest #88784

Closed

File check failures in x64 jit tests #88783

Closed

[7.0] IJW support in newer version of CMake breaks the build on empty TargetFramework #88806

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jkotas approved these changes Jul 14, 2023

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jkotas merged commit 8bf03a6 into dotnet:main Jul 14, 2023

am11 reviewed Jul 14, 2023

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VSadov deleted the pgSize branch July 14, 2023 15:33

ghost locked as resolved and limited conversation to collaborators Aug 13, 2023

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[NativeAOT] Support variable page size on Linux Arm64 #88710

[NativeAOT] Support variable page size on Linux Arm64 #88710

VSadov commented Jul 12, 2023

ghost commented Jul 12, 2023

jkotas Jul 12, 2023

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[NativeAOT] Support variable page size on Linux Arm64 #88710

[NativeAOT] Support variable page size on Linux Arm64 #88710

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