| Message ID | 20190910233146.206080-10-almasrymina@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | hugetlb_cgroup: Add hugetlb_cgroup reservation limits | expand |
On 9/10/19 5:31 PM, Mina Almasry wrote: > Add docs for how to use hugetlb_cgroup reservations, and their behavior. > > Signed-off-by: Mina Almasry <almasrymina@google.com> > Acked-by: Hillf Danton <hdanton@sina.com> > --- > .../admin-guide/cgroup-v1/hugetlb.rst | 84 ++++++++++++++++--- > 1 file changed, 73 insertions(+), 11 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v1/hugetlb.rst b/Documentation/admin-guide/cgroup-v1/hugetlb.rst > index a3902aa253a96..cc6eb859fc722 100644 > --- a/Documentation/admin-guide/cgroup-v1/hugetlb.rst > +++ b/Documentation/admin-guide/cgroup-v1/hugetlb.rst > @@ -2,13 +2,6 @@ > HugeTLB Controller > ================== > > -The HugeTLB controller allows to limit the HugeTLB usage per control group and > -enforces the controller limit during page fault. Since HugeTLB doesn't > -support page reclaim, enforcing the limit at page fault time implies that, > -the application will get SIGBUS signal if it tries to access HugeTLB pages > -beyond its limit. This requires the application to know beforehand how much > -HugeTLB pages it would require for its use. > - > HugeTLB controller can be created by first mounting the cgroup filesystem. > > # mount -t cgroup -o hugetlb none /sys/fs/cgroup > @@ -28,10 +21,14 @@ process (bash) into it. > > Brief summary of control files:: > > - hugetlb.<hugepagesize>.limit_in_bytes # set/show limit of "hugepagesize" hugetlb usage > - hugetlb.<hugepagesize>.max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded > - hugetlb.<hugepagesize>.usage_in_bytes # show current usage for "hugepagesize" hugetlb > - hugetlb.<hugepagesize>.failcnt # show the number of allocation failure due to HugeTLB limit > + hugetlb.<hugepagesize>.reservation_limit_in_bytes # set/show limit of "hugepagesize" hugetlb reservations > + hugetlb.<hugepagesize>.reservation_max_usage_in_bytes # show max "hugepagesize" hugetlb reservations recorded > + hugetlb.<hugepagesize>.reservation_usage_in_bytes # show current reservations for "hugepagesize" hugetlb > + hugetlb.<hugepagesize>.reservation_failcnt # show the number of allocation failure due to HugeTLB reservation limit > + hugetlb.<hugepagesize>.limit_in_bytes # set/show limit of "hugepagesize" hugetlb faults > + hugetlb.<hugepagesize>.max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded > + hugetlb.<hugepagesize>.usage_in_bytes # show current usage for "hugepagesize" hugetlb > + hugetlb.<hugepagesize>.failcnt # show the number of allocation failure due to HugeTLB usage limit > > For a system supporting three hugepage sizes (64k, 32M and 1G), the control > files include:: > @@ -40,11 +37,76 @@ files include:: > hugetlb.1GB.max_usage_in_bytes > hugetlb.1GB.usage_in_bytes > hugetlb.1GB.failcnt > + hugetlb.1GB.reservation_limit_in_bytes > + hugetlb.1GB.reservation_max_usage_in_bytes > + hugetlb.1GB.reservation_usage_in_bytes > + hugetlb.1GB.reservation_failcnt > hugetlb.64KB.limit_in_bytes > hugetlb.64KB.max_usage_in_bytes > hugetlb.64KB.usage_in_bytes > hugetlb.64KB.failcnt > + hugetlb.64KB.reservation_limit_in_bytes > + hugetlb.64KB.reservation_max_usage_in_bytes > + hugetlb.64KB.reservation_usage_in_bytes > + hugetlb.64KB.reservation_failcnt > hugetlb.32MB.limit_in_bytes > hugetlb.32MB.max_usage_in_bytes > hugetlb.32MB.usage_in_bytes > hugetlb.32MB.failcnt > + hugetlb.32MB.reservation_limit_in_bytes > + hugetlb.32MB.reservation_max_usage_in_bytes > + hugetlb.32MB.reservation_usage_in_bytes > + hugetlb.32MB.reservation_failcnt > + > + > +1. Reservation limits > + > +The HugeTLB controller allows to limit the HugeTLB reservations per control > +group and enforces the controller limit at reservation time. Reservation limits > +are superior to Page fault limits (see section 2), since Reservation limits are > +enforced at reservation time, and never causes the application to get SIGBUS > +signal. Instead, if the application is violating its limits, then it gets an > +error on reservation time, i.e. the mmap or shmget return an error. > + > + > +2. Page fault limits > + > +The HugeTLB controller allows to limit the HugeTLB usage (page fault) per > +control group and enforces the controller limit during page fault. Since HugeTLB > +doesn't support page reclaim, enforcing the limit at page fault time implies > +that, the application will get SIGBUS signal if it tries to access HugeTLB > +pages beyond its limit. This requires the application to know beforehand how > +much HugeTLB pages it would require for its use. > + > + > +3. Caveats with shared memory > + > +a. Charging and uncharging: > + > +For shared hugetlb memory, both hugetlb reservation and usage (page faults) are > +charged to the first task that causes the memory to be reserved or faulted, > +and all subsequent uses of this reserved or faulted memory is done without > +charging. > + > +Shared hugetlb memory is only uncharged when it is unreseved or deallocated. Spelling? > +This is usually when the hugetlbfs file is deleted, and not when the task that > +caused the reservation or fault has exited. > + > +b. Interaction between reservation limit and fault limit. > + > +Generally, it's not recommended to set both of the reservation limit and fault > +limit in a cgroup. For private memory, the fault usage cannot exceed the > +reservation usage, so if you set both, one of those limits will be useless. > + Is this enforced? What happens when attempt is made to set fault limit on a cgroup that has reservation limit and vice versa. > +For shared memory, a cgroup's fault usage may be greater than its reservation > +usage, so some care needs to be taken. Consider this example: > + > +- Task A reserves 4 pages in a shared hugetlbfs file. Cgroup A will get > + 4 reservations charged to it and no faults charged to it. > +- Task B reserves and faults the same 4 pages as Task A. Cgroup B will get no > + reservation charge, but will get charged 4 faulted pages. If Cgroup B's limit > + is less than 4, then Task B will get a SIGBUS. > + > +For the above scenario, it's not recommended for the userspace to set both > +reservation limits and fault limits, but it is still allowed to in case it sees > +some use for it. What would be the scenarios where setting both could be useful? Please explain. > -- > 2.23.0.162.g0b9fbb3734-goog > thanks, -- Shuah
diff --git a/Documentation/admin-guide/cgroup-v1/hugetlb.rst b/Documentation/admin-guide/cgroup-v1/hugetlb.rst index a3902aa253a96..cc6eb859fc722 100644 --- a/Documentation/admin-guide/cgroup-v1/hugetlb.rst +++ b/Documentation/admin-guide/cgroup-v1/hugetlb.rst @@ -2,13 +2,6 @@ HugeTLB Controller ================== -The HugeTLB controller allows to limit the HugeTLB usage per control group and -enforces the controller limit during page fault. Since HugeTLB doesn't -support page reclaim, enforcing the limit at page fault time implies that, -the application will get SIGBUS signal if it tries to access HugeTLB pages -beyond its limit. This requires the application to know beforehand how much -HugeTLB pages it would require for its use. - HugeTLB controller can be created by first mounting the cgroup filesystem. # mount -t cgroup -o hugetlb none /sys/fs/cgroup @@ -28,10 +21,14 @@ process (bash) into it. Brief summary of control files:: - hugetlb.<hugepagesize>.limit_in_bytes # set/show limit of "hugepagesize" hugetlb usage - hugetlb.<hugepagesize>.max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded - hugetlb.<hugepagesize>.usage_in_bytes # show current usage for "hugepagesize" hugetlb - hugetlb.<hugepagesize>.failcnt # show the number of allocation failure due to HugeTLB limit + hugetlb.<hugepagesize>.reservation_limit_in_bytes # set/show limit of "hugepagesize" hugetlb reservations + hugetlb.<hugepagesize>.reservation_max_usage_in_bytes # show max "hugepagesize" hugetlb reservations recorded + hugetlb.<hugepagesize>.reservation_usage_in_bytes # show current reservations for "hugepagesize" hugetlb + hugetlb.<hugepagesize>.reservation_failcnt # show the number of allocation failure due to HugeTLB reservation limit + hugetlb.<hugepagesize>.limit_in_bytes # set/show limit of "hugepagesize" hugetlb faults + hugetlb.<hugepagesize>.max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded + hugetlb.<hugepagesize>.usage_in_bytes # show current usage for "hugepagesize" hugetlb + hugetlb.<hugepagesize>.failcnt # show the number of allocation failure due to HugeTLB usage limit For a system supporting three hugepage sizes (64k, 32M and 1G), the control files include:: @@ -40,11 +37,76 @@ files include:: hugetlb.1GB.max_usage_in_bytes hugetlb.1GB.usage_in_bytes hugetlb.1GB.failcnt + hugetlb.1GB.reservation_limit_in_bytes + hugetlb.1GB.reservation_max_usage_in_bytes + hugetlb.1GB.reservation_usage_in_bytes + hugetlb.1GB.reservation_failcnt hugetlb.64KB.limit_in_bytes hugetlb.64KB.max_usage_in_bytes hugetlb.64KB.usage_in_bytes hugetlb.64KB.failcnt + hugetlb.64KB.reservation_limit_in_bytes + hugetlb.64KB.reservation_max_usage_in_bytes + hugetlb.64KB.reservation_usage_in_bytes + hugetlb.64KB.reservation_failcnt hugetlb.32MB.limit_in_bytes hugetlb.32MB.max_usage_in_bytes hugetlb.32MB.usage_in_bytes hugetlb.32MB.failcnt + hugetlb.32MB.reservation_limit_in_bytes + hugetlb.32MB.reservation_max_usage_in_bytes + hugetlb.32MB.reservation_usage_in_bytes + hugetlb.32MB.reservation_failcnt + + +1. Reservation limits + +The HugeTLB controller allows to limit the HugeTLB reservations per control +group and enforces the controller limit at reservation time. Reservation limits +are superior to Page fault limits (see section 2), since Reservation limits are +enforced at reservation time, and never causes the application to get SIGBUS +signal. Instead, if the application is violating its limits, then it gets an +error on reservation time, i.e. the mmap or shmget return an error. + + +2. Page fault limits + +The HugeTLB controller allows to limit the HugeTLB usage (page fault) per +control group and enforces the controller limit during page fault. Since HugeTLB +doesn't support page reclaim, enforcing the limit at page fault time implies +that, the application will get SIGBUS signal if it tries to access HugeTLB +pages beyond its limit. This requires the application to know beforehand how +much HugeTLB pages it would require for its use. + + +3. Caveats with shared memory + +a. Charging and uncharging: + +For shared hugetlb memory, both hugetlb reservation and usage (page faults) are +charged to the first task that causes the memory to be reserved or faulted, +and all subsequent uses of this reserved or faulted memory is done without +charging. + +Shared hugetlb memory is only uncharged when it is unreseved or deallocated. +This is usually when the hugetlbfs file is deleted, and not when the task that +caused the reservation or fault has exited. + +b. Interaction between reservation limit and fault limit. + +Generally, it's not recommended to set both of the reservation limit and fault +limit in a cgroup. For private memory, the fault usage cannot exceed the +reservation usage, so if you set both, one of those limits will be useless. + +For shared memory, a cgroup's fault usage may be greater than its reservation +usage, so some care needs to be taken. Consider this example: + +- Task A reserves 4 pages in a shared hugetlbfs file. Cgroup A will get + 4 reservations charged to it and no faults charged to it. +- Task B reserves and faults the same 4 pages as Task A. Cgroup B will get no + reservation charge, but will get charged 4 faulted pages. If Cgroup B's limit + is less than 4, then Task B will get a SIGBUS. + +For the above scenario, it's not recommended for the userspace to set both +reservation limits and fault limits, but it is still allowed to in case it sees +some use for it.