Clarify that madvise only works on full pages, and remove references to 'bytes'. Update MADV_DONTNEED and MADV_REMOVE sections to remove notes that HugeTLB mappings are not supported. They now are supported. Under 'Linux notes' describe addr requirements and length handling for ranges in HugeTLB mappings. Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> --- man2/madvise.2 | 36 ++++++++++++++++++++++++++---------- 1 file changed, 26 insertions(+), 10 deletions(-) diff --git a/man2/madvise.2 b/man2/madvise.2 index f1f384c0c..c3b0615cb 100644 --- a/man2/madvise.2 +++ b/man2/madvise.2 @@ -61,9 +61,13 @@ system call is used to give advice or directions to the kernel about the address range beginning at address .I addr and with size +.IR length . +.BR madvise () +only operates on whole pages, therefore +.I addr +must be page-aligned. The value of .I length -bytes -In most cases, +is rounded up to a multiple of page size. In most cases, the goal of such advice is to improve system or application performance. .PP Initially, the system call supported a set of "conventional" @@ -143,7 +147,7 @@ The resident set size (RSS) of the calling process will be immediately reduced however. .IP .B MADV_DONTNEED -cannot be applied to locked pages, Huge TLB pages, or +cannot be applied to locked pages, or .BR VM_PFNMAP pages. (Pages marked with the kernel-internal @@ -170,24 +174,24 @@ Note that some of these operations change the semantics of memory accesses. .\" commit f6b3ec238d12c8cc6cc71490c6e3127988460349 Free up a given range of pages and its associated backing store. -This is equivalent to punching a hole in the corresponding byte +This is equivalent to punching a hole in the corresponding range of the backing store (see .BR fallocate (2)). Subsequent accesses in the specified address range will see -bytes containing zero. +pages containing zero. .\" Databases want to use this feature to drop a section of their .\" bufferpool (shared memory segments) - without writing back to .\" disk/swap space. This feature is also useful for supporting .\" hot-plug memory on UML. .IP The specified address range must be mapped shared and writable. -This flag cannot be applied to locked pages, Huge TLB pages, or +This flag cannot be applied to locked pages, or .BR VM_PFNMAP pages. .IP In the initial implementation, only .BR tmpfs (5) -was supported +supported .BR MADV_REMOVE ; but since Linux 3.5, .\" commit 3f31d07571eeea18a7d34db9af21d2285b807a17 @@ -196,9 +200,9 @@ any filesystem which supports the .BR FALLOC_FL_PUNCH_HOLE mode also supports .BR MADV_REMOVE . -Hugetlbfs fails with the error -.BR EINVAL -and other filesystems fail with the error +Filesystems which do not support +.BR MADV_REMOVE +fail with the error .BR EOPNOTSUPP . .TP .BR MADV_DONTFORK " (since Linux 2.6.16)" @@ -596,6 +600,18 @@ that are not mapped, the Linux version of ignores them and applies the call to the rest (but returns .B ENOMEM from the system call, as it should). +.PP +If the specified address +.I addr +is within a mapping backed by Huge TLB pages, then +.I addr +must be aligned to the underlying Huge TLB page size. If the range +specified by +.I addr +and +.I length +ends in a mapping backed by Huge TLB pages, then the end of the range +will be rounded up to a multiple of the underlying Huge TLB page size. .\" .SH HISTORY .\" The .\" .BR madvise () -- 2.35.3
