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| author | Austin Clements <austin@google.com> | 2018-01-01 17:53:59 -0500 |
|---|---|---|
| committer | Austin Clements <austin@google.com> | 2018-02-15 21:12:25 +0000 |
| commit | 90666b8a3d5545f4295d9c2517ad607ce5d45e52 (patch) | |
| tree | 4242490e9767d717bbc001676af60f290cd08f48 /src/runtime/lfstack_64bit.go | |
| parent | 51ae88ee2f9a1063c272a497527751d786291c89 (diff) | |
| download | go-90666b8a3d5545f4295d9c2517ad607ce5d45e52.tar.xz | |
runtime: move comment about address space sizes to malloc.go
Currently there's a detailed comment in lfstack_64bit.go about address
space limitations on various architectures. Since that's now relevant
to malloc, move it to a more prominent place in the documentation for
memLimitBits.
Updates #10460.
Change-Id: If9708291cf3a288057b8b3ba0ba6a59e3602bbd6
Reviewed-on: https://go-review.googlesource.com/85889
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
Diffstat (limited to 'src/runtime/lfstack_64bit.go')
| -rw-r--r-- | src/runtime/lfstack_64bit.go | 25 |
1 files changed, 6 insertions, 19 deletions
diff --git a/src/runtime/lfstack_64bit.go b/src/runtime/lfstack_64bit.go index cf6c02895f..19d8045203 100644 --- a/src/runtime/lfstack_64bit.go +++ b/src/runtime/lfstack_64bit.go @@ -11,30 +11,17 @@ import "unsafe" const ( // addrBits is the number of bits needed to represent a virtual address. // - // In Linux the user address space for each architecture is limited as - // follows (taken from the processor.h file for the architecture): - // - // Architecture Name Maximum Value (exclusive) - // --------------------------------------------------------------------- - // amd64 TASK_SIZE_MAX 0x007ffffffff000 (47 bit addresses) - // arm64 TASK_SIZE_64 0x01000000000000 (48 bit addresses) - // ppc64{,le} TASK_SIZE_USER64 0x00400000000000 (46 bit addresses) - // mips64{,le} TASK_SIZE64 0x00010000000000 (40 bit addresses) - // s390x TASK_SIZE 1<<64 (64 bit addresses) - // - // These values may increase over time. In particular, ppc64 - // and mips64 support arbitrary 64-bit addresses in hardware, - // but Linux imposes the above limits. amd64 has hardware - // support for 57 bit addresses as of 2017 (56 bits for user - // space), but Linux only uses addresses above 1<<47 for - // mappings that explicitly pass a high hint address. + // See memLimitBits for a table of address space sizes on + // various architectures. 48 bits is enough for all + // architectures except s390x. // // On AMD64, virtual addresses are 48-bit (or 57-bit) numbers sign extended to 64. // We shift the address left 16 to eliminate the sign extended part and make // room in the bottom for the count. // - // On s390x, there's not much we can do, so we just hope that - // the kernel doesn't get to really high addresses. + // On s390x, virtual addresses are 64-bit. There's not much we + // can do about this, so we just hope that the kernel doesn't + // get to really high addresses and panic if it does. addrBits = 48 // In addition to the 16 bits taken from the top, we can take 3 from the |