Hey Alex!
On Mon, Oct 31, 2022 at 2:15 PM Alejandro Colomar
<alx.manpages@xxxxxxxxx> wrote:
>
> Hi Zach!
>
> On 10/22/22 00:33, Zach OKeefe wrote:
> > From: Zach O'Keefe <zokeefe@xxxxxxxxxx>
> >
> > Linux 6.1 introduced MADV_COLLAPSE in upstream commit 7d8faaf15545
> > ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse") and
> > upstream commit 34488399fa08 ("mm/madvise: add file and shmem support to
> > MADV_COLLAPSE"). Update the man-pages for madvise(2) and
> > process_madvise(2).
> >
> > Link: https://lore.kernel.org/linux-mm/20220922224046.1143204-1-zokeefe@xxxxxxxxxx/
> > Link: https://lore.kernel.org/linux-mm/20220706235936.2197195-1-zokeefe@xxxxxxxxxx/
> > Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
>
> There are a few issues with this patch:
>
> alx@asus5775:~/src/linux/man-pages/man-pages$ make lint-man-groff
> LINT (groff) tmp/lint/man2/madvise.2.lint-man.groff.touch
> eqn:man2/madvise.2:473: error: invalid input character code '128'
> eqn:man2/madvise.2:473: error: invalid input character code '153'
> an.tmac:man2/madvise.2:445: style: .BR expects at least 2 arguments, got 1
> an.tmac:man2/madvise.2:456: style: .BR expects at least 2 arguments, got 1
> an.tmac:man2/madvise.2:463: style: .BR expects at least 2 arguments, got 1
> found style problems; aborting
> make: *** [lib/lint-man.mk:77: tmp/lint/man2/madvise.2.lint-man.groff.touch] Error 1
>
>
> Let's investigate them:
>
Thank you :)
> alx@asus5775:~/src/linux/man-pages/man-pages$ sed -n 473p man2/madvise.2
> this operation will be deemed successful.
>
> This one was a bit difficult to track, since the line count seems to be off by one:
>
> alx@asus5775:~/src/linux/man-pages/man-pages$ tbl man2/madvise.2 | hd | grep -C1
> ' 80 '
> 00003d40 63 65 73 73 66 75 6c 2e 0a 4e 6f 74 65 20 74 68 |cessful..Note th|
> 00003d50 61 74 20 74 68 69 73 20 64 6f 65 73 6e e2 80 99 |at this doesn...|
> 00003d60 74 20 67 75 61 72 61 6e 74 65 65 20 61 6e 79 74 |t guarantee anyt|
> alx@asus5775:~/src/linux/man-pages/man-pages$ sed -n 474p man2/madvise.2
> Note that this doesn’t guarantee anything about other possible mappings of
>
> The issue was in line 474, and the issue is that it uses a weird single quote.
> Please use the foillowing ASCII character for the single quote (see ascii(7)):
> 047 39 27 '
>
Very weird and good find! Honestly, I had prototyped this in Google
Docs and copy-pasta'd this over as the basis. I tried testing this
again - and same thing - Google Docs uses some other character.
Anyways - glad you caught this.
> The rest of issues seems trivial:
> Use .B instead of .BR because there's no "roman" (i.e., non-bold) part.
>
This was the first time it clicked what ".BR" meant: "bold followed by roman".
> alx@asus5775:~/src/linux/man-pages/man-pages$ sed -n 445p man2/madvise.2
> .BR MADV_COLLAPSE
> alx@asus5775:~/src/linux/man-pages/man-pages$ sed -n 456p man2/madvise.2
> .BR MADV_COLLAPSE
> alx@asus5775:~/src/linux/man-pages/man-pages$ sed -n 463p man2/madvise.2
> .BR VM_NOHUGEPAGE
>
These didn't show up with my version of groff (as in 1/2), but I've
applied the fixes and sent out a v4 for this patch. Again, thank you
for all your help here!
Best,
Zach
>
> I'll report a bug to groff(1) about the issue with the line count.
>
Ya that's an odd one. Sorry for having to encounter this - must have
been quite confusing. Thank you!
> Cheers,
>
> Alex
>
> > ---
> > man2/madvise.2 | 90 +++++++++++++++++++++++++++++++++++++++++-
> > man2/process_madvise.2 | 10 +++++
> > 2 files changed, 98 insertions(+), 2 deletions(-)
> >
> > diff --git a/man2/madvise.2 b/man2/madvise.2
> > index df3413cc8..b03fc731d 100644
> > --- a/man2/madvise.2
> > +++ b/man2/madvise.2
> > @@ -385,9 +385,10 @@ set (see
> > .BR prctl (2) ).
> > .IP
> > The
> > -.B MADV_HUGEPAGE
> > +.BR MADV_HUGEPAGE ,
> > +.BR MADV_NOHUGEPAGE ,
> > and
> > -.B MADV_NOHUGEPAGE
> > +.B MADV_COLLAPSE
> > operations are available only if the kernel was configured with
> > .B CONFIG_TRANSPARENT_HUGEPAGE
> > and file/shmem memory is only supported if the kernel was configured with
> > @@ -400,6 +401,81 @@ and
> > .I length
> > will not be backed by transparent hugepages.
> > .TP
> > +.BR MADV_COLLAPSE " (since Linux 6.1)"
> > +.\" commit 7d8faaf155454f8798ec56404faca29a82689c77
> > +.\" commit 34488399fa08faaf664743fa54b271eb6f9e1321
> > +Perform a best-effort synchronous collapse of the native pages mapped by the
> > +memory range into Transparent Huge Pages (THPs).
> > +.B MADV_COLLAPSE
> > +operates on the current state of memory of the calling process and makes no
> > +persistent changes or guarantees on how pages will be mapped,
> > +constructed,
> > +or faulted in the future.
> > +.IP
> > +.B MADV_COLLAPSE
> > +supports private anonymous pages (see
> > +.BR mmap (2)),
> > +shmem pages,
> > +and file-backed pages.
> > +See
> > +.B MADV_HUGEPAGE
> > +for general information on memory requirements for THP.
> > +If the range provided spans multiple VMAs,
> > +the semantics of the collapse over each VMA is independent from the others.
> > +If collapse of a given huge page-aligned/sized region fails,
> > +the operation may continue to attempt collapsing the remainder of the
> > +specified memory.
> > +.B MADV_COLLAPSE
> > +will automatically clamp the provided range to be hugepage-aligned.
> > +.IP
> > +All non-resident pages covered by the range will first be
> > +swapped/faulted-in,
> > +before being copied onto a freshly allocated hugepage.
> > +If the native pages compose the same PTE-mapped hugepage,
> > +and are suitably aligned,
> > +allocation of a new hugepage may be elided and collapse may happen
> > +in-place.
> > +Unmapped pages will have their data directly initialized to 0 in the new
> > +hugepage.
> > +However,
> > +for every eligible hugepage-aligned/sized region to be collapsed,
> > +at least one page must currently be backed by physical memory.
> > +.IP
> > +.BR MADV_COLLAPSE
> > +is independent of any sysfs
> > +(see
> > +.BR sysfs (5))
> > +setting under
> > +.IR /sys/kernel/mm/transparent_hugepage ,
> > +both in terms of determining THP eligibility,
> > +and allocation semantics.
> > +See Linux kernel source file
> > +.I Documentation/admin\-guide/mm/transhuge.rst
> > +for more information.
> > +.BR MADV_COLLAPSE
> > +also ignores
> > +.B huge=
> > +tmpfs mount when operating on tmpfs files.
> > +Allocation for the new hugepage may enter direct reclaim and/or compaction,
> > +regardless of VMA flags
> > +(though
> > +.BR VM_NOHUGEPAGE
> > +is still respected).
> > +.IP
> > +When the system has multiple NUMA nodes,
> > +the hugepage will be allocated from the node providing the most native
> > +pages.
> > +.IP
> > +If all hugepage-sized/aligned regions covered by the provided range were
> > +either successfully collapsed,
> > +or were already PMD-mapped THPs,
> > +this operation will be deemed successful.
> > +Note that this doesn’t guarantee anything about other possible mappings of
> > +the memory.
> > +Also note that many failures might have occurred since the operation may
> > +continue to collapse in the event collapse of a single hugepage-sized/aligned
> > +region fails.
> > +.TP
> > .BR MADV_DONTDUMP " (since Linux 3.4)"
> > .\" commit 909af768e88867016f427264ae39d27a57b6a8ed
> > .\" commit accb61fe7bb0f5c2a4102239e4981650f9048519
> > @@ -619,6 +695,11 @@ A kernel resource was temporarily unavailable.
> > .B EBADF
> > The map exists, but the area maps something that isn't a file.
> > .TP
> > +.B EBUSY
> > +(for
> > +.BR MADV_COLLAPSE )
> > +Could not charge hugepage to cgroup: cgroup limit exceeded.
> > +.TP
> > .B EFAULT
> > .I advice
> > is
> > @@ -716,6 +797,11 @@ maximum resident set size.
> > Not enough memory: paging in failed.
> > .TP
> > .B ENOMEM
> > +(for
> > +.BR MADV_COLLAPSE )
> > +Not enough memory: could not allocate hugepage.
> > +.TP
> > +.B ENOMEM
> > Addresses in the specified range are not currently
> > mapped, or are outside the address space of the process.
> > .TP
> > diff --git a/man2/process_madvise.2 b/man2/process_madvise.2
> > index 44d3b94e8..8b0ddccdd 100644
> > --- a/man2/process_madvise.2
> > +++ b/man2/process_madvise.2
> > @@ -73,6 +73,10 @@ argument is one of the following values:
> > See
> > .BR madvise (2).
> > .TP
> > +.B MADV_COLLAPSE
> > +See
> > +.BR madvise (2).
> > +.TP
> > .B MADV_PAGEOUT
> > See
> > .BR madvise (2).
> > @@ -173,6 +177,12 @@ The caller does not have permission to access the address space of the process
> > .TP
> > .B ESRCH
> > The target process does not exist (i.e., it has terminated and been waited on).
> > +.PP
> > +See
> > +.BR madvise (2)
> > +for
> > +.IR advice -specific
> > +errors.
> > .SH VERSIONS
> > This system call first appeared in Linux 5.10.
> > .\" commit ecb8ac8b1f146915aa6b96449b66dd48984caacc
>
> --
> <http://www.alejandro-colomar.es/>
