On Mon, Oct 17, 2022 at 2:41 AM Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Oct 13, 2022 at 01:16:31PM -0700, Yang Shi wrote: > > On Thu, Oct 13, 2022 at 5:38 AM Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Wed, Oct 05, 2022 at 11:03:39AM -0700, Yang Shi wrote: > > > > Since v5.13 the page bulk allocator was introduced to allocate order-0 > > > > pages in bulk. There are a few mempool allocator callers which does > > > > order-0 page allocation in a loop, for example, dm-crypt, f2fs compress, > > > > etc. A mempool page bulk allocator seems useful. So introduce the > > > > mempool page bulk allocator. > > > > > > > > It introduces the below APIs: > > > > - mempool_init_pages_bulk() > > > > - mempool_create_pages_bulk() > > > > They initialize the mempool for page bulk allocator. The pool is filled > > > > by alloc_page() in a loop. > > > > > > > > - mempool_alloc_pages_bulk_list() > > > > - mempool_alloc_pages_bulk_array() > > > > They do bulk allocation from mempool. > > > > They do the below conceptually: > > > > 1. Call bulk page allocator > > > > 2. If the allocation is fulfilled then return otherwise try to > > > > allocate the remaining pages from the mempool > > > > 3. If it is fulfilled then return otherwise retry from #1 with sleepable > > > > gfp > > > > 4. If it is still failed, sleep for a while to wait for the mempool is > > > > refilled, then retry from #1 > > > > The populated pages will stay on the list or array until the callers > > > > consume them or free them. > > > > Since mempool allocator is guaranteed to success in the sleepable context, > > > > so the two APIs return true for success or false for fail. It is the > > > > caller's responsibility to handle failure case (partial allocation), just > > > > like the page bulk allocator. > > > > > > > > The mempool typically is an object agnostic allocator, but bulk allocation > > > > is only supported by pages, so the mempool bulk allocator is for page > > > > allocation only as well. > > > > > > > > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> > > > > > > Overall, I think it's an ok approach and certainly a good use case for > > > the bulk allocator. > > > > > > The main concern that I have is that the dm-crypt use case doesn't really > > > want to use lists as such and it's just a means for collecting pages to pass > > > to bio_add_page(). bio_add_page() is working with arrays but you cannot > > > use that array directly as any change to how that array is populated will > > > then explode. Unfortunately, what you have is adding pages to a list to > > > take them off the list and put them in an array and that is inefficient. > > > > Yeah, I didn't think of a better way to pass the pages to dm-crypt. > > > > > > > > How about this > > > > > > 1. Add a callback to __alloc_pages_bulk() that takes a page as a > > > parameter like bulk_add_page() or whatever. > > > > > > 2. For page_list == NULL && page_array == NULL, the callback is used > > > > > > 3. Add alloc_pages_bulk_cb() that passes in the name of a callback > > > function > > > > > > 4. In the dm-crypt case, use the callback to pass the page to bio_add_page > > > for the new page allocated. > > > > Thank you so much for the suggestion. But I have a hard time > > understanding how these work together. Do you mean call bio_add_page() > > in the callback? But bio_add_page() needs other parameters. Or I > > misunderstood you? > > > > I expected dm-crypt to define the callback. Using bio_add_page > directly would not work as the bulk allocator has no idea what to pass > bio_add_page. dm-crypt would likely need to create both a callback and an > opaque data structure passed as (void *) to track "clone" and "len" I see. Yeah, we have to pass the "clone" and "len" to the callback via pool_data. It should not be hard since dm-crypt already uses crypt_config to maintain a counter for allocated pages, we should just need to pass the struct to the callback as a parameter. But I'm wondering whether this is worth it or not? Will it make the code harder to follow? > > -- > Mel Gorman > SUSE Labs
