Ryo Tsuruta wrote: > Hi, > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Date: Fri, 17 Apr 2009 11:24:33 +0900 > >> On Fri, 17 Apr 2009 10:49:43 +0900 >> Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx> wrote: >> >>> Hi, >>> >>> I have a few question. >>> - I have not yet fully understood how your controller are using >>> bio_cgroup. If my view is wrong please tell me. >>> >>> o In my view, bio_cgroup's implementation strongly depends on >>> page_cgoup's. Could you explain for what purpose does this >>> functionality itself should be implemented as cgroup subsystem? >>> Using page_cgoup and implementing tracking APIs is not enough? >> I'll definitely do "Nack" to add full bio-cgroup members to page_cgroup. >> Now, page_cgroup is 40bytes(in 64bit arch.) And all of them are allocated at >> boot time as memmap. (and add member to struct page is much harder ;) >> >> IIUC, feature for "tracking bio" is just necesary for pages for I/O. >> So, I think it's much better to add misc. information to struct bio not to the page. >> But, if people want to add "small hint" to struct page or struct page_cgroup >> for tracking buffered I/O, I'll give you help as much as I can. >> Maybe using "unused bits" in page_cgroup->flags is a choice with no overhead. > > In the case where the bio-cgroup data is allocated dynamically, > - Sometimes quite a large amount of memory get marked dirty. > In this case it requires more kernel memory than that of the > current implementation. > - The operation is expansive due to memory allocations and exclusive > controls by such as spinlocks. > > In the case where the bio-cgroup data is allocated by delayed allocation, > - It makes the operation complicated and expensive, because > sometimes a bio has to be created in the context of other > processes, such as aio and swap-out operation. > > I'd prefer a simple and lightweight implementation. bio-cgroup only > needs 4bytes unlike memory controller. The reason why bio-cgroup chose > this approach is to minimize the overhead. Elaborating on Yoshikawa-san's comment, I would like to propose a generic I/O tracking mechanism that is not tied to all the cgroup paraphernalia. This approach has several advantages: - By using this functionality, existing I/O schedulers (well, some relatively minor changes would be needed) would be able to schedule buffered I/O properly. - The amount of memory consumed to do the tracking could be optimized according to the kernel configuration (do we really need struct page_cgroup when the cgroup memory controller or all of the cgroup infrastructure has been configured out?). The I/O tracking functionality would look something like the following: - Create an API to acquire the I/O context of a certain page, which is cgroup independent. For discussion purposes, I will assume that the I/O context of a page is the io_context of the task that dirtied the page (this can be changed if deemed necessary, though). - When cgroups are not being used, pages would be tracked using a pfn-indexed array of struct io_context (à la memcg's array of struct page_cgroup). - When cgroups are activated but the memory controller is not, we would have a pfn-indexed array of struct blkio_cgroup, which would have both a pointer to the corresponding io_context of the page and a reference to the cgroup it belongs to (most likely using css_id). The API offered by the I/O tracking mechanism would be extended so that the kernel can easily obtain not only the per-task io_context but also the cgroup a certain page belongs to. Please notice that by doing this we have all the information we need to schedule buffered I/O both at the cgroup-level and the task-level. From the memory usage point of view, memory controller-specific bits would be gone and to top it all we save one indirection level (since struct page_cgroup would be out of the picture). - When the memory controller is active we would have the pfn-indexed array of struct page_cgroup we have know plus a reference to the corresponding cgroup and io_context (yes, I still want to do proper scheduling of buffered I/O within a cgroup). - Finally, since bio entering the block layer can generate additional bios it is necessary to pass the I/O context information of original bio down to the new bios. For that stacking devices such as dm and those of that ilk will have to be modified. To improve performance I/O context information would be cached in bios (to achieve this we have to ensure that all bios that enter the block layer have the right I/O context information attached to it). Yoshikawa-san and myself have been working on a patch-set that implements just this and we have reached that point where the kernel does not panic right after booting:), so we will be sending patches soon (hopefully this weekend). Any thoughts? Regards, Fernando _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
