[PATCH] madvise.2: Document MADV_POPULATE_READ and MADV_POPULATE_WRITE

[David Hildenbrand]

Let's document MADV_POPULATE_READ and MADV_POPULATE_WRITE behavior and
error conditions.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Richard Henderson <rth@xxxxxxxxxxx>
Cc: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>
Cc: Matt Turner <mattst88@xxxxxxxxx>
Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Cc: "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: Chris Zankel <chris@xxxxxxxxxx>
Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Rolf Eike Beer <eike-kernel@xxxxxxxxx>
Cc: linux-alpha@xxxxxxxxxxxxxxx
Cc: linux-mips@xxxxxxxxxxxxxxx
Cc: linux-parisc@xxxxxxxxxxxxxxx
Cc: linux-xtensa@xxxxxxxxxxxxxxxx
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: Linux API <linux-api@xxxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---

Not for upstream man pages yet, only for linux-mm and linux-api review
purposes. Once/if the linux changes are merged upstream, I'll send it to
the proper man list/maintainers.

---
 man2/madvise.2 | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)

diff --git a/man2/madvise.2 b/man2/madvise.2
index f1f384c0c..3ec8c53a7 100644
--- a/man2/madvise.2
+++ b/man2/madvise.2
@@ -469,6 +469,59 @@ If a page is file-backed and dirty, it will be written back to the backing
 storage.
 The advice might be ignored for some pages in the range when it is not
 applicable.
+.TP
+.BR MADV_POPULATE_READ " (since Linux 5.14)
+Populate (prefault) page tables readable for the whole range without actually
+reading. Depending on the underlying mapping, map the shared zeropage,
+preallocate memory or read the underlying file; files with holes might or
+might not preallocate blocks.
+Do not generate
+.B SIGBUS
+when populating fails, return an error instead.
+.IP
+If
+.B MADV_POPULATE_READ
+succeeds, all page tables have been populated (prefaulted) readable once.
+If
+.B MADV_POPULATE_READ
+fails, some page tables might have been populated.
+.IP
+.B MADV_POPULATE_READ
+cannot be applied to mappings without read permissions
+and special mappings marked with the kernel-internal
+.B VM_PFNMAP
+and
+.BR VM_IO .
+.IP
+Note that with
+.BR MADV_POPULATE_READ ,
+the process can be killed at any moment when the system runs out of memory.
+.TP
+.BR MADV_POPULATE_WRITE " (since Linux 5.14)
+Populate (prefault) page tables writable for the whole range without actually
+writing. Depending on the underlying mapping, preallocate memory or read the
+underlying file; files with holes will preallocate blocks.
+Do not generate
+.B SIGBUS
+when populating fails, return an error instead.
+.IP
+If
+.B MADV_POPULATE_WRITE
+succeeds, all page tables have been populated (prefaulted) writable once.
+If
+.B MADV_POPULATE_WRITE
+fails, some page tables might have been populated.
+.IP
+.B MADV_POPULATE_WRITE
+cannot be applied to mappings without write permissions
+and special mappings marked with the kernel-internal
+.B VM_PFNMAP
+and
+.BR VM_IO .
+.IP
+Note that
+.BR MADV_POPULATE_WRITE ,
+the process can be killed at any moment when the system runs out of memory.
 .SH RETURN VALUE
 On success,
 .BR madvise ()
@@ -533,6 +586,17 @@ or
 .BR VM_PFNMAP
 ranges.
 .TP
+.B EINVAL
+.I advice
+is
+.B MADV_POPULATE_READ
+or
+.BR MADV_POPULATE_WRITE ,
+but the specified address range includes ranges with insufficient permissions,
+.B VM_IO
+or
+.BR VM_PFNMAP.
+.TP
 .B EIO
 (for
 .BR MADV_WILLNEED )
@@ -548,6 +612,14 @@ Not enough memory: paging in failed.
 Addresses in the specified range are not currently
 mapped, or are outside the address space of the process.
 .TP
+.B ENOMEM
+.I advice
+is
+.B MADV_POPULATE_READ
+or
+.BR MADV_POPULATE_WRITE ,
+but populating (prefaulting) page tables failed.
+.TP
 .B EPERM
 .I advice
 is
@@ -555,6 +627,14 @@ is
 but the caller does not have the
 .B CAP_SYS_ADMIN
 capability.
+.TP
+.B EHWPOISON
+.I advice
+is
+.B MADV_POPULATE_READ
+or
+.BR MADV_POPULATE_WRITE ,
+and a HW poisoned page is encountered.
 .SH VERSIONS
 Since Linux 3.18,
 .\" commit d3ac21cacc24790eb45d735769f35753f5b56ceb
-- 
2.31.1