[v9,1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter
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Message ID 20191217231615.164161-1-almasrymina@google.com
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  • [v9,1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter
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Commit Message

Mina Almasry Dec. 17, 2019, 11:16 p.m. UTC
These counters will track hugetlb reservations rather than hugetlb
memory faulted in. This patch only adds the counter, following patches
add the charging and uncharging of the counter.

This is patch 1 of an 8 patch series.

Problem:
Currently tasks attempting to allocate more hugetlb memory than is available get
a failure at mmap/shmget time. This is thanks to Hugetlbfs Reservations [1].
However, if a task attempts to allocate hugetlb memory only more than its
hugetlb_cgroup limit allows, the kernel will allow the mmap/shmget call,
but will SIGBUS the task when it attempts to fault the memory in.

We have developers interested in using hugetlb_cgroups, and they have expressed
dissatisfaction regarding this behavior. We'd like to improve this
behavior such that tasks violating the hugetlb_cgroup limits get an error on
mmap/shmget time, rather than getting SIGBUS'd when they try to fault
the excess memory in.

The underlying problem is that today's hugetlb_cgroup accounting happens
at hugetlb memory *fault* time, rather than at *reservation* time.
Thus, enforcing the hugetlb_cgroup limit only happens at fault time, and
the offending task gets SIGBUS'd.

Proposed Solution:
A new page counter named hugetlb.xMB.reservation_[limit|usage]_in_bytes. This
counter has slightly different semantics than
hugetlb.xMB.[limit|usage]_in_bytes:

- While usage_in_bytes tracks all *faulted* hugetlb memory,
reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
hugetlb memory faulted in without a prior reservation.

- If a task attempts to reserve more memory than limit_in_bytes allows,
the kernel will allow it to do so. But if a task attempts to reserve
more memory than reservation_limit_in_bytes, the kernel will fail this
reservation.

This proposal is implemented in this patch series, with tests to verify
functionality and show the usage. We also added cgroup-v2 support to
hugetlb_cgroup so that the new use cases can be extended to v2.

Alternatives considered:
1. A new cgroup, instead of only a new page_counter attached to
   the existing hugetlb_cgroup. Adding a new cgroup seemed like a lot of code
   duplication with hugetlb_cgroup. Keeping hugetlb related page counters under
   hugetlb_cgroup seemed cleaner as well.

2. Instead of adding a new counter, we considered adding a sysctl that modifies
   the behavior of hugetlb.xMB.[limit|usage]_in_bytes, to do accounting at
   reservation time rather than fault time. Adding a new page_counter seems
   better as userspace could, if it wants, choose to enforce different cgroups
   differently: one via limit_in_bytes, and another via
   reservation_limit_in_bytes. This could be very useful if you're
   transitioning how hugetlb memory is partitioned on your system one
   cgroup at a time, for example. Also, someone may find usage for both
   limit_in_bytes and reservation_limit_in_bytes concurrently, and this
   approach gives them the option to do so.

Testing:
- Added tests passing.
- Used libhugetlbfs for regression testing.

[1]: https://www.kernel.org/doc/html/latest/vm/hugetlbfs_reserv.html

Signed-off-by: Mina Almasry <almasrymina@google.com>
Acked-by: Hillf Danton <hdanton@sina.com>

---
 include/linux/hugetlb.h |   4 +-
 mm/hugetlb_cgroup.c     | 116 +++++++++++++++++++++++++++++++++++-----
 2 files changed, 106 insertions(+), 14 deletions(-)

--
2.24.1.735.g03f4e72817-goog

Comments

Andrew Morton Dec. 19, 2019, 1:12 a.m. UTC | #1
On Tue, 17 Dec 2019 15:16:08 -0800 Mina Almasry <almasrymina@google.com> wrote:

> These counters will track hugetlb reservations rather than hugetlb
> memory faulted in. This patch only adds the counter, following patches
> add the charging and uncharging of the counter.
> 
> This is patch 1 of an 8 patch series.
> 
> Problem:
> Currently tasks attempting to allocate more hugetlb memory than is available get
> a failure at mmap/shmget time. This is thanks to Hugetlbfs Reservations [1].
> However, if a task attempts to allocate hugetlb memory only more than its
> hugetlb_cgroup limit allows, the kernel will allow the mmap/shmget call,
> but will SIGBUS the task when it attempts to fault the memory in.
> 
> We have developers interested in using hugetlb_cgroups, and they have expressed
> dissatisfaction regarding this behavior. We'd like to improve this
> behavior such that tasks violating the hugetlb_cgroup limits get an error on
> mmap/shmget time, rather than getting SIGBUS'd when they try to fault
> the excess memory in.
> 
> The underlying problem is that today's hugetlb_cgroup accounting happens
> at hugetlb memory *fault* time, rather than at *reservation* time.
> Thus, enforcing the hugetlb_cgroup limit only happens at fault time, and
> the offending task gets SIGBUS'd.
> 
> Proposed Solution:
> A new page counter named hugetlb.xMB.reservation_[limit|usage]_in_bytes. This
> counter has slightly different semantics than
> hugetlb.xMB.[limit|usage]_in_bytes:
> 
> - While usage_in_bytes tracks all *faulted* hugetlb memory,
> reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
> hugetlb memory faulted in without a prior reservation.
> 
> - If a task attempts to reserve more memory than limit_in_bytes allows,
> the kernel will allow it to do so. But if a task attempts to reserve
> more memory than reservation_limit_in_bytes, the kernel will fail this
> reservation.
> 
> This proposal is implemented in this patch series, with tests to verify
> functionality and show the usage. We also added cgroup-v2 support to
> hugetlb_cgroup so that the new use cases can be extended to v2.

This would make
http://lkml.kernel.org/r/20191216193831.540953-1-gscrivan@redhat.com
obsolete?


> Alternatives considered:
> 1. A new cgroup, instead of only a new page_counter attached to
>    the existing hugetlb_cgroup. Adding a new cgroup seemed like a lot of code
>    duplication with hugetlb_cgroup. Keeping hugetlb related page counters under
>    hugetlb_cgroup seemed cleaner as well.
> 
> 2. Instead of adding a new counter, we considered adding a sysctl that modifies
>    the behavior of hugetlb.xMB.[limit|usage]_in_bytes, to do accounting at
>    reservation time rather than fault time. Adding a new page_counter seems
>    better as userspace could, if it wants, choose to enforce different cgroups
>    differently: one via limit_in_bytes, and another via
>    reservation_limit_in_bytes. This could be very useful if you're
>    transitioning how hugetlb memory is partitioned on your system one
>    cgroup at a time, for example. Also, someone may find usage for both
>    limit_in_bytes and reservation_limit_in_bytes concurrently, and this
>    approach gives them the option to do so.
>
Mike Kravetz Dec. 19, 2019, 1:37 a.m. UTC | #2
On 12/18/19 5:12 PM, Andrew Morton wrote:
> On Tue, 17 Dec 2019 15:16:08 -0800 Mina Almasry <almasrymina@google.com> wrote:
<snip>
>> This proposal is implemented in this patch series, with tests to verify
>> functionality and show the usage. We also added cgroup-v2 support to
>> hugetlb_cgroup so that the new use cases can be extended to v2.
> 
> This would make
> http://lkml.kernel.org/r/20191216193831.540953-1-gscrivan@redhat.com
> obsolete?

I haven't started looking at this series yet.  However, since Mina was
involved in the discussion of that patch (hugetlb controller for cgroups v2)
my assumption is that this patch would simply build on that v2 support?
Seems like the above patch would be a prereq for this series.

Mina, are those assumptions correct and perhaps this is an old/obsolete
comment?  Does this series apply 'on top' of the above patch?  That patch
is already in Andrew's tree.
Mina Almasry Dec. 19, 2019, 1:59 a.m. UTC | #3
On Wed, Dec 18, 2019 at 5:37 PM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 12/18/19 5:12 PM, Andrew Morton wrote:
> > On Tue, 17 Dec 2019 15:16:08 -0800 Mina Almasry <almasrymina@google.com> wrote:
> <snip>
> >> This proposal is implemented in this patch series, with tests to verify
> >> functionality and show the usage. We also added cgroup-v2 support to
> >> hugetlb_cgroup so that the new use cases can be extended to v2.
> >
> > This would make
> > http://lkml.kernel.org/r/20191216193831.540953-1-gscrivan@redhat.com
> > obsolete?
>
> I haven't started looking at this series yet.  However, since Mina was
> involved in the discussion of that patch (hugetlb controller for cgroups v2)
> my assumption is that this patch would simply build on that v2 support?
> Seems like the above patch would be a prereq for this series.
>
> Mina, are those assumptions correct and perhaps this is an old/obsolete
> comment?  Does this series apply 'on top' of the above patch?  That patch
> is already in Andrew's tree.

Gah, I just forgot to update this commit message. This patch series is
indeed on top of Giuseppe's v2 support and doesn't conflict or
duplicate that functionality. Sorry for the confusion. I'll fix the
commit message in the next iteration.

> --
> Mike Kravetz
Mike Kravetz Jan. 13, 2020, 6:43 p.m. UTC | #4
On 12/17/19 3:16 PM, Mina Almasry wrote:
> These counters will track hugetlb reservations rather than hugetlb
> memory faulted in. This patch only adds the counter, following patches
> add the charging and uncharging of the counter.
> 
> This is patch 1 of an 8 patch series.
> 
> Problem:
> Currently tasks attempting to allocate more hugetlb memory than is available get
> a failure at mmap/shmget time. This is thanks to Hugetlbfs Reservations [1].
> However, if a task attempts to allocate hugetlb memory only more than its
> hugetlb_cgroup limit allows, the kernel will allow the mmap/shmget call,
> but will SIGBUS the task when it attempts to fault the memory in.
> 
> We have developers interested in using hugetlb_cgroups, and they have expressed
> dissatisfaction regarding this behavior. We'd like to improve this
> behavior such that tasks violating the hugetlb_cgroup limits get an error on
> mmap/shmget time, rather than getting SIGBUS'd when they try to fault
> the excess memory in.
> 
> The underlying problem is that today's hugetlb_cgroup accounting happens
> at hugetlb memory *fault* time, rather than at *reservation* time.
> Thus, enforcing the hugetlb_cgroup limit only happens at fault time, and
> the offending task gets SIGBUS'd.
> 
> Proposed Solution:
> A new page counter named hugetlb.xMB.reservation_[limit|usage]_in_bytes. This
> counter has slightly different semantics than
> hugetlb.xMB.[limit|usage]_in_bytes:
> 
> - While usage_in_bytes tracks all *faulted* hugetlb memory,
> reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
> hugetlb memory faulted in without a prior reservation.

To me, this implies that 'faults without reservations' could cause
reservation usage to exceed reservation limit?  Or, does the faulting
process get a SIGBUS because of the reservation limit even though it
is not using reservations?

We shall see in subsequent patches.

> 
> - If a task attempts to reserve more memory than limit_in_bytes allows,
> the kernel will allow it to do so. But if a task attempts to reserve
> more memory than reservation_limit_in_bytes, the kernel will fail this
> reservation.
> 
> This proposal is implemented in this patch series, with tests to verify
> functionality and show the usage. We also added cgroup-v2 support to
> hugetlb_cgroup so that the new use cases can be extended to v2.

As previously discussed, cgroup-v2 support for hugetlb_cgroup will exist
before this patch series.

> 
> Alternatives considered:
> 1. A new cgroup, instead of only a new page_counter attached to
>    the existing hugetlb_cgroup. Adding a new cgroup seemed like a lot of code
>    duplication with hugetlb_cgroup. Keeping hugetlb related page counters under
>    hugetlb_cgroup seemed cleaner as well.
> 
> 2. Instead of adding a new counter, we considered adding a sysctl that modifies
>    the behavior of hugetlb.xMB.[limit|usage]_in_bytes, to do accounting at
>    reservation time rather than fault time. Adding a new page_counter seems
>    better as userspace could, if it wants, choose to enforce different cgroups
>    differently: one via limit_in_bytes, and another via
>    reservation_limit_in_bytes. This could be very useful if you're
>    transitioning how hugetlb memory is partitioned on your system one
>    cgroup at a time, for example. Also, someone may find usage for both
>    limit_in_bytes and reservation_limit_in_bytes concurrently, and this
>    approach gives them the option to do so.
> 
> Testing:
> - Added tests passing.
> - Used libhugetlbfs for regression testing.
> 
> [1]: https://www.kernel.org/doc/html/latest/vm/hugetlbfs_reserv.html
> 
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> Acked-by: Hillf Danton <hdanton@sina.com>

I think the ACK by Hillf happened some time back.  You may want to check
to see if it still applies.

> 
> ---
>  include/linux/hugetlb.h |   4 +-
>  mm/hugetlb_cgroup.c     | 116 +++++++++++++++++++++++++++++++++++-----
>  2 files changed, 106 insertions(+), 14 deletions(-)

Only one minor nit in the code.

You made this cleanup,
@@ -472,7 +519,7 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
        struct hstate *h = &hstates[idx];

        /* format the size */
-       mem_fmt(buf, 32, huge_page_size(h));
+       mem_fmt(buf, sizeof(buf), huge_page_size(h));

        /* Add the limit file */
        cft = &h->cgroup_files_dfl[0];

But did not make the same cleanup in __hugetlb_cgroup_file_legacy_init()
Mina Almasry Jan. 13, 2020, 9:03 p.m. UTC | #5
On Mon, Jan 13, 2020 at 10:44 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 12/17/19 3:16 PM, Mina Almasry wrote:
> > These counters will track hugetlb reservations rather than hugetlb
> > memory faulted in. This patch only adds the counter, following patches
> > add the charging and uncharging of the counter.
> >
> > This is patch 1 of an 8 patch series.
> >
> > Problem:
> > Currently tasks attempting to allocate more hugetlb memory than is available get
> > a failure at mmap/shmget time. This is thanks to Hugetlbfs Reservations [1].
> > However, if a task attempts to allocate hugetlb memory only more than its
> > hugetlb_cgroup limit allows, the kernel will allow the mmap/shmget call,
> > but will SIGBUS the task when it attempts to fault the memory in.
> >
> > We have developers interested in using hugetlb_cgroups, and they have expressed
> > dissatisfaction regarding this behavior. We'd like to improve this
> > behavior such that tasks violating the hugetlb_cgroup limits get an error on
> > mmap/shmget time, rather than getting SIGBUS'd when they try to fault
> > the excess memory in.
> >
> > The underlying problem is that today's hugetlb_cgroup accounting happens
> > at hugetlb memory *fault* time, rather than at *reservation* time.
> > Thus, enforcing the hugetlb_cgroup limit only happens at fault time, and
> > the offending task gets SIGBUS'd.
> >
> > Proposed Solution:
> > A new page counter named hugetlb.xMB.reservation_[limit|usage]_in_bytes. This
> > counter has slightly different semantics than
> > hugetlb.xMB.[limit|usage]_in_bytes:
> >
> > - While usage_in_bytes tracks all *faulted* hugetlb memory,
> > reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
> > hugetlb memory faulted in without a prior reservation.
>
> To me, this implies that 'faults without reservations' could cause
> reservation usage to exceed reservation limit?  Or, does the faulting
> process get a SIGBUS because of the reservation limit even though it
> is not using reservations?
>
> We shall see in subsequent patches.
>

The design we went with based on previous discussions is as follows:
hugetlb pages faulted without a prior reservation get accounted at
fault time, rather than reservation time, and if the fault causes the
counter to cross the limit, the charge fails, hence the fault fails,
hence the process gets sigbus'd.

This means that one counter I'm adding here can cover both use cases:
if the userspace uses MAP_NORESERVE, then their memory is accounted at
fault time and they may get sigbus'd. If the userspace does *not* use
MAP_NORESERVE, then their memory is charged at reservation (mmap) time
and should be completely immune to runtime sigbus, unless they do
something really weird like reserve a bunch of memory, punch a hole in
the reserved memory, lower their limit, then fault in memory from the
hole.

> >
> > - If a task attempts to reserve more memory than limit_in_bytes allows,
> > the kernel will allow it to do so. But if a task attempts to reserve
> > more memory than reservation_limit_in_bytes, the kernel will fail this
> > reservation.
> >
> > This proposal is implemented in this patch series, with tests to verify
> > functionality and show the usage. We also added cgroup-v2 support to
> > hugetlb_cgroup so that the new use cases can be extended to v2.
>
> As previously discussed, cgroup-v2 support for hugetlb_cgroup will exist
> before this patch series.
>

Yes, this will be fixed in the next iteration.

> >
> > Alternatives considered:
> > 1. A new cgroup, instead of only a new page_counter attached to
> >    the existing hugetlb_cgroup. Adding a new cgroup seemed like a lot of code
> >    duplication with hugetlb_cgroup. Keeping hugetlb related page counters under
> >    hugetlb_cgroup seemed cleaner as well.
> >
> > 2. Instead of adding a new counter, we considered adding a sysctl that modifies
> >    the behavior of hugetlb.xMB.[limit|usage]_in_bytes, to do accounting at
> >    reservation time rather than fault time. Adding a new page_counter seems
> >    better as userspace could, if it wants, choose to enforce different cgroups
> >    differently: one via limit_in_bytes, and another via
> >    reservation_limit_in_bytes. This could be very useful if you're
> >    transitioning how hugetlb memory is partitioned on your system one
> >    cgroup at a time, for example. Also, someone may find usage for both
> >    limit_in_bytes and reservation_limit_in_bytes concurrently, and this
> >    approach gives them the option to do so.
> >
> > Testing:
> > - Added tests passing.
> > - Used libhugetlbfs for regression testing.
> >
> > [1]: https://www.kernel.org/doc/html/latest/vm/hugetlbfs_reserv.html
> >
> > Signed-off-by: Mina Almasry <almasrymina@google.com>
> > Acked-by: Hillf Danton <hdanton@sina.com>
>
> I think the ACK by Hillf happened some time back.  You may want to check
> to see if it still applies.
>

Yes, will remove the ack in the next iteration. I'll re-add it if Hilf
reviews again.

> >
> > ---
> >  include/linux/hugetlb.h |   4 +-
> >  mm/hugetlb_cgroup.c     | 116 +++++++++++++++++++++++++++++++++++-----
> >  2 files changed, 106 insertions(+), 14 deletions(-)
>
> Only one minor nit in the code.
>
> You made this cleanup,
> @@ -472,7 +519,7 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
>         struct hstate *h = &hstates[idx];
>
>         /* format the size */
> -       mem_fmt(buf, 32, huge_page_size(h));
> +       mem_fmt(buf, sizeof(buf), huge_page_size(h));
>
>         /* Add the limit file */
>         cft = &h->cgroup_files_dfl[0];
>
> But did not make the same cleanup in __hugetlb_cgroup_file_legacy_init()

Will be fixed in the next iteration.

> --
> Mike Kravetz
Mike Kravetz Jan. 13, 2020, 10:05 p.m. UTC | #6
On 1/13/20 1:03 PM, Mina Almasry wrote:
> On Mon, Jan 13, 2020 at 10:44 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>>
>> On 12/17/19 3:16 PM, Mina Almasry wrote:
>>> - While usage_in_bytes tracks all *faulted* hugetlb memory,
>>> reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
>>> hugetlb memory faulted in without a prior reservation.
>>
>> To me, this implies that 'faults without reservations' could cause
>> reservation usage to exceed reservation limit?  Or, does the faulting
>> process get a SIGBUS because of the reservation limit even though it
>> is not using reservations?
>>
>> We shall see in subsequent patches.
>>
> 
> The design we went with based on previous discussions is as follows:
> hugetlb pages faulted without a prior reservation get accounted at
> fault time, rather than reservation time, and if the fault causes the
> counter to cross the limit, the charge fails, hence the fault fails,
> hence the process gets sigbus'd.

Ok, sorry I did not recall the design discussion.

> This means that one counter I'm adding here can cover both use cases:
> if the userspace uses MAP_NORESERVE, then their memory is accounted at
> fault time and they may get sigbus'd.

Let's make sure this is clearly documented.  Someone could be surprised
if their application not using reserves gets a SIGBUS because there is a
reserve limit.
Mina Almasry Jan. 13, 2020, 10:21 p.m. UTC | #7
> >> On 12/17/19 3:16 PM, Mina Almasry wrote:
> >
> > The design we went with based on previous discussions is as follows:
> > hugetlb pages faulted without a prior reservation get accounted at
> > fault time, rather than reservation time, and if the fault causes the
> > counter to cross the limit, the charge fails, hence the fault fails,
> > hence the process gets sigbus'd.
>
> Ok, sorry I did not recall the design discussion.
>

No worries! It has indeed been a while since that discussion.

> > This means that one counter I'm adding here can cover both use cases:
> > if the userspace uses MAP_NORESERVE, then their memory is accounted at
> > fault time and they may get sigbus'd.
>
> Let's make sure this is clearly documented.  Someone could be surprised
> if their application not using reserves gets a SIGBUS because there is a
> reserve limit.

I have some stuff on that already in the docs patch, but I'll beef
that section up to ensure there is no confusion.
David Rientjes Jan. 14, 2020, 12:45 a.m. UTC | #8
On Tue, 17 Dec 2019, Mina Almasry wrote:

> These counters will track hugetlb reservations rather than hugetlb
> memory faulted in. This patch only adds the counter, following patches
> add the charging and uncharging of the counter.
> 
> This is patch 1 of an 8 patch series.
> 
> Problem:
> Currently tasks attempting to allocate more hugetlb memory than is available get
> a failure at mmap/shmget time. This is thanks to Hugetlbfs Reservations [1].
> However, if a task attempts to allocate hugetlb memory only more than its
> hugetlb_cgroup limit allows, the kernel will allow the mmap/shmget call,
> but will SIGBUS the task when it attempts to fault the memory in.
> 

I think it's subtle, but the use of the word "allocate" instead of using 
"reserve" might be confusing here.  Might want to reword it.

> We have developers interested in using hugetlb_cgroups, and they have expressed
> dissatisfaction regarding this behavior. We'd like to improve this
> behavior such that tasks violating the hugetlb_cgroup limits get an error on
> mmap/shmget time, rather than getting SIGBUS'd when they try to fault
> the excess memory in.
> 

I'm not sure the developers are interested in being restricted by 
hugetlb_cgroups :)  I think users get constrained by hugetlb_cgroup so the 
developers are interested in the failure more: do we want to SIGBUS at 
fault and not be allowed an opportunity to influence that (today) or do we 
want to fallback to non-hugetlbfs memory and just keep going (tomorrow, 
after your patchset).

> The underlying problem is that today's hugetlb_cgroup accounting happens
> at hugetlb memory *fault* time, rather than at *reservation* time.
> Thus, enforcing the hugetlb_cgroup limit only happens at fault time, and
> the offending task gets SIGBUS'd.
> 
> Proposed Solution:
> A new page counter named hugetlb.xMB.reservation_[limit|usage]_in_bytes. This
> counter has slightly different semantics than
> hugetlb.xMB.[limit|usage]_in_bytes:
> 

Is there a max_usage_in_bytes equivalent?  It's a page_counter so I assume 
it's easy to support.

I'll defer the naming to Mike here, "rsvd" seems to be the hugetlb way of 
saying "reserved".

> - While usage_in_bytes tracks all *faulted* hugetlb memory,
> reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
> hugetlb memory faulted in without a prior reservation.
> 
> - If a task attempts to reserve more memory than limit_in_bytes allows,
> the kernel will allow it to do so. But if a task attempts to reserve
> more memory than reservation_limit_in_bytes, the kernel will fail this
> reservation.
> 
> This proposal is implemented in this patch series, with tests to verify
> functionality and show the usage. We also added cgroup-v2 support to
> hugetlb_cgroup so that the new use cases can be extended to v2.
> 
> Alternatives considered:
> 1. A new cgroup, instead of only a new page_counter attached to
>    the existing hugetlb_cgroup. Adding a new cgroup seemed like a lot of code
>    duplication with hugetlb_cgroup. Keeping hugetlb related page counters under
>    hugetlb_cgroup seemed cleaner as well.
> 
> 2. Instead of adding a new counter, we considered adding a sysctl that modifies
>    the behavior of hugetlb.xMB.[limit|usage]_in_bytes, to do accounting at
>    reservation time rather than fault time. Adding a new page_counter seems
>    better as userspace could, if it wants, choose to enforce different cgroups
>    differently: one via limit_in_bytes, and another via
>    reservation_limit_in_bytes. This could be very useful if you're
>    transitioning how hugetlb memory is partitioned on your system one
>    cgroup at a time, for example. Also, someone may find usage for both
>    limit_in_bytes and reservation_limit_in_bytes concurrently, and this
>    approach gives them the option to do so.
> 
> Testing:
> - Added tests passing.
> - Used libhugetlbfs for regression testing.
> 
> [1]: https://www.kernel.org/doc/html/latest/vm/hugetlbfs_reserv.html
> 
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> Acked-by: Hillf Danton <hdanton@sina.com>

Patch
diff mbox series

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 1e897e4168ac1..dea6143aa0685 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -432,8 +432,8 @@  struct hstate {
 	unsigned int surplus_huge_pages_node[MAX_NUMNODES];
 #ifdef CONFIG_CGROUP_HUGETLB
 	/* cgroup control files */
-	struct cftype cgroup_files_dfl[5];
-	struct cftype cgroup_files_legacy[5];
+	struct cftype cgroup_files_dfl[7];
+	struct cftype cgroup_files_legacy[9];
 #endif
 	char name[HSTATE_NAME_LEN];
 };
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index e434b05416c68..35415af9ed26f 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -36,6 +36,11 @@  struct hugetlb_cgroup {
 	 */
 	struct page_counter hugepage[HUGE_MAX_HSTATE];

+	/*
+	 * the counter to account for hugepage reservations from hugetlb.
+	 */
+	struct page_counter reserved_hugepage[HUGE_MAX_HSTATE];
+
 	atomic_long_t events[HUGE_MAX_HSTATE][HUGETLB_NR_MEMORY_EVENTS];
 	atomic_long_t events_local[HUGE_MAX_HSTATE][HUGETLB_NR_MEMORY_EVENTS];

@@ -55,6 +60,14 @@  struct hugetlb_cgroup {

 static struct hugetlb_cgroup *root_h_cgroup __read_mostly;

+static inline struct page_counter *
+hugetlb_cgroup_get_counter(struct hugetlb_cgroup *h_cg, int idx, bool reserved)
+{
+	if (reserved)
+		return &h_cg->reserved_hugepage[idx];
+	return &h_cg->hugepage[idx];
+}
+
 static inline
 struct hugetlb_cgroup *hugetlb_cgroup_from_css(struct cgroup_subsys_state *s)
 {
@@ -295,28 +308,42 @@  void hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,

 enum {
 	RES_USAGE,
+	RES_RESERVATION_USAGE,
 	RES_LIMIT,
+	RES_RESERVATION_LIMIT,
 	RES_MAX_USAGE,
+	RES_RESERVATION_MAX_USAGE,
 	RES_FAILCNT,
+	RES_RESERVATION_FAILCNT,
 };

 static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,
 				   struct cftype *cft)
 {
 	struct page_counter *counter;
+	struct page_counter *reserved_counter;
 	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(css);

 	counter = &h_cg->hugepage[MEMFILE_IDX(cft->private)];
+	reserved_counter = &h_cg->reserved_hugepage[MEMFILE_IDX(cft->private)];

 	switch (MEMFILE_ATTR(cft->private)) {
 	case RES_USAGE:
 		return (u64)page_counter_read(counter) * PAGE_SIZE;
+	case RES_RESERVATION_USAGE:
+		return (u64)page_counter_read(reserved_counter) * PAGE_SIZE;
 	case RES_LIMIT:
 		return (u64)counter->max * PAGE_SIZE;
+	case RES_RESERVATION_LIMIT:
+		return (u64)reserved_counter->max * PAGE_SIZE;
 	case RES_MAX_USAGE:
 		return (u64)counter->watermark * PAGE_SIZE;
+	case RES_RESERVATION_MAX_USAGE:
+		return (u64)reserved_counter->watermark * PAGE_SIZE;
 	case RES_FAILCNT:
 		return counter->failcnt;
+	case RES_RESERVATION_FAILCNT:
+		return reserved_counter->failcnt;
 	default:
 		BUG();
 	}
@@ -338,10 +365,16 @@  static int hugetlb_cgroup_read_u64_max(struct seq_file *seq, void *v)
 			   1 << huge_page_order(&hstates[idx]));

 	switch (MEMFILE_ATTR(cft->private)) {
+	case RES_RESERVATION_USAGE:
+		counter = &h_cg->reserved_hugepage[idx];
+		/* Fall through. */
 	case RES_USAGE:
 		val = (u64)page_counter_read(counter);
 		seq_printf(seq, "%llu\n", val * PAGE_SIZE);
 		break;
+	case RES_RESERVATION_LIMIT:
+		counter = &h_cg->reserved_hugepage[idx];
+		/* Fall through. */
 	case RES_LIMIT:
 		val = (u64)counter->max;
 		if (val == limit)
@@ -365,6 +398,7 @@  static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
 	int ret, idx;
 	unsigned long nr_pages;
 	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(of_css(of));
+	bool reserved = false;

 	if (hugetlb_cgroup_is_root(h_cg)) /* Can't set limit on root */
 		return -EINVAL;
@@ -378,9 +412,14 @@  static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
 	nr_pages = round_down(nr_pages, 1 << huge_page_order(&hstates[idx]));

 	switch (MEMFILE_ATTR(of_cft(of)->private)) {
+	case RES_RESERVATION_LIMIT:
+		reserved = true;
+		/* Fall through. */
 	case RES_LIMIT:
 		mutex_lock(&hugetlb_limit_mutex);
-		ret = page_counter_set_max(&h_cg->hugepage[idx], nr_pages);
+		ret = page_counter_set_max(hugetlb_cgroup_get_counter(h_cg, idx,
+								      reserved),
+					   nr_pages);
 		mutex_unlock(&hugetlb_limit_mutex);
 		break;
 	default:
@@ -406,18 +445,26 @@  static ssize_t hugetlb_cgroup_reset(struct kernfs_open_file *of,
 				    char *buf, size_t nbytes, loff_t off)
 {
 	int ret = 0;
-	struct page_counter *counter;
+	struct page_counter *counter, *reserved_counter;
 	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(of_css(of));

 	counter = &h_cg->hugepage[MEMFILE_IDX(of_cft(of)->private)];
+	reserved_counter =
+		&h_cg->reserved_hugepage[MEMFILE_IDX(of_cft(of)->private)];

 	switch (MEMFILE_ATTR(of_cft(of)->private)) {
 	case RES_MAX_USAGE:
 		page_counter_reset_watermark(counter);
 		break;
+	case RES_RESERVATION_MAX_USAGE:
+		page_counter_reset_watermark(reserved_counter);
+		break;
 	case RES_FAILCNT:
 		counter->failcnt = 0;
 		break;
+	case RES_RESERVATION_FAILCNT:
+		reserved_counter->failcnt = 0;
+		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -472,7 +519,7 @@  static void __init __hugetlb_cgroup_file_dfl_init(int idx)
 	struct hstate *h = &hstates[idx];

 	/* format the size */
-	mem_fmt(buf, 32, huge_page_size(h));
+	mem_fmt(buf, sizeof(buf), huge_page_size(h));

 	/* Add the limit file */
 	cft = &h->cgroup_files_dfl[0];
@@ -482,15 +529,30 @@  static void __init __hugetlb_cgroup_file_dfl_init(int idx)
 	cft->write = hugetlb_cgroup_write_dfl;
 	cft->flags = CFTYPE_NOT_ON_ROOT;

-	/* Add the current usage file */
+	/* Add the reservation limit file */
 	cft = &h->cgroup_files_dfl[1];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.reservation_max", buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_LIMIT);
+	cft->seq_show = hugetlb_cgroup_read_u64_max;
+	cft->write = hugetlb_cgroup_write_dfl;
+	cft->flags = CFTYPE_NOT_ON_ROOT;
+
+	/* Add the current usage file */
+	cft = &h->cgroup_files_dfl[2];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.current", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_USAGE);
 	cft->seq_show = hugetlb_cgroup_read_u64_max;
 	cft->flags = CFTYPE_NOT_ON_ROOT;

+	/* Add the current reservation usage file */
+	cft = &h->cgroup_files_dfl[3];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.reservation_current", buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_USAGE);
+	cft->seq_show = hugetlb_cgroup_read_u64_max;
+	cft->flags = CFTYPE_NOT_ON_ROOT;
+
 	/* Add the events file */
-	cft = &h->cgroup_files_dfl[2];
+	cft = &h->cgroup_files_dfl[4];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.events", buf);
 	cft->private = MEMFILE_PRIVATE(idx, 0);
 	cft->seq_show = hugetlb_events_show;
@@ -498,7 +560,7 @@  static void __init __hugetlb_cgroup_file_dfl_init(int idx)
 	cft->flags = CFTYPE_NOT_ON_ROOT;

 	/* Add the events.local file */
-	cft = &h->cgroup_files_dfl[3];
+	cft = &h->cgroup_files_dfl[5];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.events.local", buf);
 	cft->private = MEMFILE_PRIVATE(idx, 0);
 	cft->seq_show = hugetlb_events_local_show;
@@ -507,7 +569,7 @@  static void __init __hugetlb_cgroup_file_dfl_init(int idx)
 	cft->flags = CFTYPE_NOT_ON_ROOT;

 	/* NULL terminate the last cft */
-	cft = &h->cgroup_files_dfl[4];
+	cft = &h->cgroup_files_dfl[6];
 	memset(cft, 0, sizeof(*cft));

 	WARN_ON(cgroup_add_dfl_cftypes(&hugetlb_cgrp_subsys,
@@ -530,28 +592,58 @@  static void __init __hugetlb_cgroup_file_legacy_init(int idx)
 	cft->read_u64 = hugetlb_cgroup_read_u64;
 	cft->write = hugetlb_cgroup_write_legacy;

-	/* Add the usage file */
+	/* Add the reservation limit file */
 	cft = &h->cgroup_files_legacy[1];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.reservation_limit_in_bytes",
+		 buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_LIMIT);
+	cft->read_u64 = hugetlb_cgroup_read_u64;
+	cft->write = hugetlb_cgroup_write_legacy;
+
+	/* Add the usage file */
+	cft = &h->cgroup_files_legacy[2];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.usage_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_USAGE);
 	cft->read_u64 = hugetlb_cgroup_read_u64;

+	/* Add the reservation usage file */
+	cft = &h->cgroup_files_legacy[3];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.reservation_usage_in_bytes",
+		 buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_USAGE);
+	cft->read_u64 = hugetlb_cgroup_read_u64;
+
 	/* Add the MAX usage file */
-	cft = &h->cgroup_files_legacy[2];
+	cft = &h->cgroup_files_legacy[4];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.max_usage_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_MAX_USAGE);
 	cft->write = hugetlb_cgroup_reset;
 	cft->read_u64 = hugetlb_cgroup_read_u64;

+	/* Add the MAX reservation usage file */
+	cft = &h->cgroup_files_legacy[5];
+	snprintf(cft->name, MAX_CFTYPE_NAME,
+		 "%s.reservation_max_usage_in_bytes", buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_MAX_USAGE);
+	cft->write = hugetlb_cgroup_reset;
+	cft->read_u64 = hugetlb_cgroup_read_u64;
+
 	/* Add the failcntfile */
-	cft = &h->cgroup_files_legacy[3];
+	cft = &h->cgroup_files_legacy[6];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.failcnt", buf);
-	cft->private  = MEMFILE_PRIVATE(idx, RES_FAILCNT);
+	cft->private = MEMFILE_PRIVATE(idx, RES_FAILCNT);
+	cft->write = hugetlb_cgroup_reset;
+	cft->read_u64 = hugetlb_cgroup_read_u64;
+
+	/* Add the reservation failcntfile */
+	cft = &h->cgroup_files_legacy[7];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.reservation_failcnt", buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_FAILCNT);
 	cft->write = hugetlb_cgroup_reset;
 	cft->read_u64 = hugetlb_cgroup_read_u64;

 	/* NULL terminate the last cft */
-	cft = &h->cgroup_files_legacy[4];
+	cft = &h->cgroup_files_legacy[8];
 	memset(cft, 0, sizeof(*cft));

 	WARN_ON(cgroup_add_legacy_cftypes(&hugetlb_cgrp_subsys,