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runtime: add physHugePageShift

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This change adds physHugePageShift which is defined such that
1 << physHugePageShift == physHugePageSize. The purpose of this variable
is to avoid doing expensive divisions in key functions, such as
(*mspan).hugePages.

This change also does a sweep of any place we might do a division or mod
operation with physHugePageSize and turns it into bit shifts and other
bitwise operations.

Finally, this change adds a check to mallocinit which ensures that
physHugePageSize is always a power of two. osinit might choose to ignore
non-powers-of-two for the value and replace it with zero, but mallocinit
will fail if it's not a power of two (or zero). It also derives
physHugePageShift from physHugePageSize.

This change helps improve the performance of most applications because
of how often (*mspan).hugePages is called.

Updates #32828.

Change-Id: I1a6db113d52d563f59ae8fd4f0e130858859e68f
Reviewed-on: https://go-review.googlesource.com/c/go/+/186598
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Michael Anthony Knyszek 2019-07-16 20:36:33 +00:00 • committed by Austin Clements
parent fbb819ebc4
commit a41ebe6e25
4 changed files with 29 additions and 9 deletions
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24
src/runtime/malloc.go
View file

@ -325,12 +325,21 @@ const (
var physPageSize uintptr
// physHugePageSize is the size in bytes of the OS's default physical huge
// page size whose allocation is opaque to the application.
// page size whose allocation is opaque to the application. It is assumed
// and verified to be a power of two.
//
// If set, this must be set by the OS init code (typically in osinit) before
// mallocinit. However, setting it at all is optional, and leaving the default
// value is always safe (though potentially less efficient).
var physHugePageSize uintptr
//
// Since physHugePageSize is always assumed to be a power of two,
// physHugePageShift is defined as physHugePageSize == 1 << physHugePageShift.
// The purpose of physHugePageShift is to avoid doing divisions in
// performance critical functions.
var (
physHugePageSize uintptr
physHugePageShift uint
)
// OS memory management abstraction layer
//
@ -432,6 +441,17 @@ func mallocinit() {
print("system page size (", physPageSize, ") must be a power of 2\n")
throw("bad system page size")
}
if physHugePageSize&(physHugePageSize-1) != 0 {
print("system huge page size (", physHugePageSize, ") must be a power of 2\n")
throw("bad system huge page size")
}
if physHugePageSize != 0 {
// Since physHugePageSize is a power of 2, it suffices to increase
// physHugePageShift until 1<<physHugePageShift == physHugePageSize.
for 1<<physHugePageShift != physHugePageSize {
physHugePageShift++
}
}
// Initialize the heap.
mheap_.init()