Hello, On Fri, Jun 05, 2015 at 11:38:42PM +0200, Arianna Avanzini wrote: > The block IO (blkio) controller enables the block layer to provide service > guarantees in a hierarchical fashion. Specifically, service guarantees > are provided by registered request-accounting policies. As of now, a > proportional-share and a throttling policy are available. They are > implemented, respectively, by the CFQ I/O scheduler and the blk-throttle > subsystem. Unfortunately, as for adding new policies, the current > implementation of the block IO controller is only halfway ready to allow > new policies to be plugged in. This commit provides a solution to make > the block IO controller fully ready to handle new policies. > In what follows, we first describe briefly the current state, and then > list the changes made by this commit. > > The throttling policy does not need any per-cgroup information to perform > its task. In contrast, the proportional share policy uses, for each cgroup, > both the weight assigned by the user to the cgroup, and a set of dynamically- > computed weights, one for each device. > > The first, user-defined weight is stored in the blkcg data structure: the > block IO controller allocates a private blkcg data structure for each > cgroup in the blkio cgroups hierarchy (regardless of which policy is active). > In other words, the block IO controller internally mirrors the blkio cgroups > with private blkcg data structures. > > On the other hand, for each cgroup and device, the corresponding dynamically- > computed weight is maintained in the following, different way. For each > device, > the block IO controller keeps a private blkcg_gq structure for each cgroup in > blkio. In other words, block IO also keeps one private mirror copy of the > blkio > cgroups hierarchy for each device, made of blkcg_gq structures. > Each blkcg_gq structure keeps per-policy information in a generic array of > dynamically-allocated 'dedicated' data structures, one for each registered > policy (so currently the array contains two elements). To be inserted into the > generic array, each dedicated data structure embeds a generic blkg_policy_data > structure. Consider now the array contained in the blkcg_gq structure > corresponding to a given pair of cgroup and device: one of the elements > of the array contains the dedicated data structure for the proportional-share > policy, and this dedicated data structure contains the dynamically-computed > weight for that pair of cgroup and device. > > The generic strategy adopted for storing per-policy data in blkcg_gq > structures > is already capable of handling new policies, whereas the one adopted with > blkcg > structures is not, because per-policy data are hard-coded in the blkcg > structures themselves (currently only data related to the proportional- > share policy). > > This commit addresses the above issues through the following changes: > . It generalizes blkcg structures so that per-policy data are stored in the > same > way as in blkcg_gq structures. > Specifically, it lets also the blkcg structure store per-policy data in a > generic array of dynamically-allocated dedicated data structures. We will > refer to these data structures as blkcg dedicated data structures, to > distinguish them from the dedicated data structures inserted in the generic > arrays kept by blkcg_gq structures. > To allow blkcg dedicated data structures to be inserted in the generic array > inside a blkcg structure, this commit also introduces a new > blkcg_policy_data > structure, which is the equivalent of blkg_policy_data for blkcg dedicated > data structures. > . It adds to the blkcg_policy structure, i.e., to the descriptor of a policy, > a > cpd_size field and a cpd_init field, to be initialized by the policy with, > respectively, the size of the blkcg dedicated data structures, and the > address of a constructor function for blkcg dedicated data structures. > . It moves the CFQ-specific fields embedded in the blkcg data structure (i.e., > the fields related to the proportional-share policy), into a new blkcg > dedicated data structure called cfq_group_data. > > Signed-off-by: Paolo Valente <paolo.vale...@unimore.it> > Signed-off-by: Arianna Avanzini <avanzini.aria...@gmail.com> > Cc: Tejun Heo <t...@kernel.org> > Cc: Jens Axboe <ax...@fb.com>
Acked-by: Tejun Heo <t...@kernel.org> Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
