Hey Zach! On 10/31/22 23:55, 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>
Okay, now I have some more comments:- A few changes about semantic newlines. See a diff at the bottom of this email that you can apply.
- An accident. - Some paragraph I don't really understand. Cheers, Alex
--- v3[1] -> v4 - Rebased to latest master - (Alejandro Colomar) Fixed weird, non-ascii chars: e2 80 99 -> "'" - (Alejandro Colomar) Replaced .BR with .B directive when the entire line was bold (no non-bold part) [1] https://lore.kernel.org/linux-man/bb3b5c3c-3966-ea1a-6d84-4f7f3afa37ca@xxxxxxxxx/T/#u man2/madvise | 0 man2/madvise.2 | 90 +++++++++++++++++++++++++++++++++++++++++- man2/process_madvise.2 | 10 +++++ 3 files changed, 98 insertions(+), 2 deletions(-) create mode 100644 man2/madvise diff --git a/man2/madvise b/man2/madvise new file mode 100644 index 000000000..e69de29bb
Heh! This was a funny accident. I realized because autocomplete showed it as a possibility. :)
The diff at the bottom removes it.
diff --git a/man2/madvise.2 b/man2/madvise.2 index edf805740..dca42c7d6 100644 --- a/man2/madvise.2 +++ b/man2/madvise.2 @@ -386,9 +386,10 @@ 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 @@ -401,6 +402,81 @@ 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 +.B 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. +.B 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 +.B 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.
I don't understand this last paragraph (since "Also note ..."). Could you please reword it a little bit?
+.TP .BR MADV_DONTDUMP " (since Linux 3.4)" .\" commit 909af768e88867016f427264ae39d27a57b6a8ed .\" commit accb61fe7bb0f5c2a4102239e4981650f9048519 @@ -620,6 +696,11 @@ 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 @@ -717,6 +798,11 @@ 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 ac98850a9..92878286b 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
Diff for changing a few line breaks (and removing the spurious file): diff --git a/man2/madvise b/man2/madvise deleted file mode 100644 index e69de29bb..000000000 diff --git a/man2/madvise.2 b/man2/madvise.2 index dca42c7d6..7f34301d3 100644 --- a/man2/madvise.2 +++ b/man2/madvise.2 @@ -405,11 +405,12 @@ .SS Linux-specific advice values .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). +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, +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 @@ -424,20 +425,20 @@ .SS Linux-specific advice values 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. +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, +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. +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. @@ -464,15 +465,15 @@ .SS Linux-specific advice values is still respected). .IP When the system has multiple NUMA nodes, -the hugepage will be allocated from the node providing the most native -pages. +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. +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. -- <http://www.alejandro-colomar.es/>
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