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: 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 ofThe 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 ' The rest of issues seems trivial: Use .B instead of .BR because there's no "roman" (i.e., non-bold) part. 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 I'll report a bug to groff(1) about the issue with the line count. 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/>
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