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. Indicate the releases when they were first supported as well as alignment restrictions. Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Peter Xu <peterx@xxxxxxxxxx> --- v2 -> v3 Rebased on man-pages-5.19-rc1. Minor change to wording for sunsequent access of data after MADV_REMOVE. v1 -> v2 Added releases when Huge TLB support was added and moved alignment requirements to corresponding section. (Peter) man2/madvise.2 | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-) diff --git a/man2/madvise.2 b/man2/madvise.2 index 2a8f1cd0a..becddce93 100644 --- a/man2/madvise.2 +++ b/man2/madvise.2 @@ -44,9 +44,13 @@ 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" @@ -126,7 +130,7 @@ 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 .B VM_PFNMAP pages. (Pages marked with the kernel-internal @@ -136,6 +140,11 @@ flag are special memory areas that are not managed by the virtual memory subsystem. Such pages are typically created by device drivers that map the pages into user space.) +.IP +Support for Huge TLB pages was added in Linux v5.18. Addresses within a +mapping backed by Huge TLB pages must be aligned to the underlying Huge TLB +page size, and the range length is rounded up to a multiple of the underlying +Huge TLB page size. .\" .\" ====================================================================== .\" @@ -153,24 +162,24 @@ 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. +data with a value of 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 .B 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 @@ -179,10 +188,12 @@ any filesystem which supports the .B FALLOC_FL_PUNCH_HOLE mode also supports .BR MADV_REMOVE . -Hugetlbfs fails with the error -.B EINVAL -and other filesystems fail with the error +Filesystems which do not support +.BR MADV_REMOVE +fail with the error .BR EOPNOTSUPP . +.IP +Support for Huge TLB filesystem was added in Linux v4.3. .TP .BR MADV_DONTFORK " (since Linux 2.6.16)" .\" commit f822566165dd46ff5de9bf895cfa6c51f53bb0c4 -- 2.35.3
