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? > > It's not free because there will be an additional function call for every > page bulk allocated but I suspect that's cheaper than adding a pile of > pages to a list just to take them off again. It also avoids adding a user > for the bulk allocator list interface that does not even want a list. > > It might mean that there is additional cleanup work for __alloc_pages_bulk > to abstract away whether a list, array or cb is used but nothing > impossible. > > -- > Mel Gorman > SUSE Labs
