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    Subject[PATCH RFC] madvise.2: Document MADV_POPULATE
    Date
    Preview of MADV_POPULATE documentation, which is still under discussion:
    https://lkml.kernel.org/r/20210217154844.12392-1-david@redhat.com

    Once/if merged, there will be an official patch to man-page folks.

    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Oscar Salvador <osalvador@suse.de>
    Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Jann Horn <jannh@google.com>
    Cc: Jason Gunthorpe <jgg@ziepe.ca>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Rik van Riel <riel@surriel.com>
    Cc: Michael S. Tsirkin <mst@redhat.com>
    Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: Richard Henderson <rth@twiddle.net>
    Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
    Cc: Matt Turner <mattst88@gmail.com>
    Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
    Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
    Cc: Helge Deller <deller@gmx.de>
    Cc: Chris Zankel <chris@zankel.net>
    Cc: Max Filippov <jcmvbkbc@gmail.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Rolf Eike Beer <eike-kernel@sf-tec.de>
    Cc: linux-alpha@vger.kernel.org
    Cc: linux-mips@vger.kernel.org
    Cc: linux-parisc@vger.kernel.org
    Cc: linux-xtensa@linux-xtensa.org
    Cc: linux-arch@vger.kernel.org
    Cc: Linux API <linux-api@vger.kernel.org>
    Signed-off-by: David Hildenbrand <david@redhat.com>
    ---
    man2/madvise.2 | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++
    1 file changed, 59 insertions(+)

    diff --git a/man2/madvise.2 b/man2/madvise.2
    index 2af407212..ff08768a3 100644
    --- a/man2/madvise.2
    +++ b/man2/madvise.2
    @@ -469,6 +469,48 @@ 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 " (since Linux 5.13)
    +Populate (prefault) page tables for the whole range.
    +Depending on the underlying mapping, preallocate memory or read the
    +underlying file.
    +Do not generate
    +.B SIGBUS
    +when populating fails, return an error instead.
    +The populate semantics match
    +.BR MAP_POPULATE
    +(see
    +.BR mmap (2))
    +with the exception that
    +.B MADV_POPULATE
    +fails if there is a proplem populating page tables.
    +.B MADV_POPULATE
    +simulates user space access to all pages in the range without actually
    +reading/writing the pages.
    +For private, writable mappings, simulate a write access; for all other
    +mappings, simulate a read access.
    +.IP
    +If
    +.B MADV_POPULATE
    +succeeds, all page tables have been populated (prefaulted) once.
    +If
    +.B MADV_POPULATE
    +fails, some page tables might have been populated.
    +.IP
    +.B MADV_POPULATE
    +cannot be applied to
    +.B PROT_NONE
    +and special mappings marked with the kernel-internal
    +.B VM_PFNMAP
    +and
    +.BR VM_IO .
    +.IP
    +Note that
    +.B MADV_POPULATE
    +will ignore any poisoned pages in the range.
    +Similar to
    +.BR MAP_POPULATE ,
    +it cannot protect from the OOM (Out Of Memory) handler killing the process.
    .SH RETURN VALUE
    On success,
    .BR madvise ()
    @@ -533,6 +575,17 @@ or
    .BR VM_PFNMAP
    ranges.
    .TP
    +.B EINVAL
    +.I advice
    +is
    +.BR MADV_POPULATE ,
    +but the specified address range includes
    +.BR PROT_NONE ,
    +.B VM_IO
    +or
    +.B VM_PFNMAP
    +ranges.
    +.TP
    .B EIO
    (for
    .BR MADV_WILLNEED )
    @@ -548,6 +601,12 @@ 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
    +.BR MADV_POPULATE ,
    +but populating (prefaulting) page tables failed.
    +.TP
    .B EPERM
    .I advice
    is
    --
    2.29.2
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