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From: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-man@vger.kernel.org,
	Alejandro Colomar <alx.manpages@gmail.com>,
	 Michael Kerrisk <mtk.manpages@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Michal Hocko <mhocko@suse.com>,
	Oscar Salvador <osalvador@suse.de>, Jann Horn <jannh@google.com>,
	 Mike Rapoport <rppt@kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	 Linux MM <linux-mm@kvack.org>
Subject: Re: [PATCH v1] madvise.2: Document MADV_POPULATE_READ and MADV_POPULATE_WRITE
Date: Mon, 12 Jul 2021 11:58:20 +0200	[thread overview]
Message-ID: <CAM9Jb+g7a5kY4DHzDzJTfs-mVEm_CFRcCeY2zdjo6sZWxkjnLA@mail.gmail.com> (raw)
In-Reply-To: <20210712083917.16361-1-david@redhat.com>

> MADV_POPULATE_READ and MADV_POPULATE_WRITE have been merged into
> upstream Linux via commit 4ca9b3859dac ("mm/madvise: introduce
> MADV_POPULATE_(READ|WRITE) to prefault page tables"), part of v5.14-rc1.
>
> Let's document the behavior and error conditions of these new madvise()
> options.
>
> Cc: Alejandro Colomar <alx.manpages@gmail.com>
> Cc: Michael Kerrisk <mtk.manpages@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Jann Horn <jannh@google.com>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Linux API <linux-api@vger.kernel.org>
> Cc: linux-mm@kvack.org
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  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

Is this read or write?
just reading and trying to understand :)

> +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
>
>


  reply	other threads:[~2021-07-12  9:58 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-12  8:39 David Hildenbrand
2021-07-12  9:58 ` Pankaj Gupta [this message]
2021-07-12 10:03   ` David Hildenbrand
2021-07-12 10:17     ` Pankaj Gupta
2021-07-25 20:15   ` Alejandro Colomar (man-pages)
2021-07-26  7:11     ` David Hildenbrand
2021-07-12 11:05 ` Pankaj Gupta

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