Hi, all In current implementation, grow_buffers() uses alloc_page() to allocate the buffers for each stripe_head, i.e. allocate a page for each dev[i] in stripe_head. After setting stripe_size as a configurable value by writing sysfs entry, it means that we always allocate 64K buffers, but just use 4K of them when stripe_size is 4K in 64KB arm64. To save memory, we try to let multiple buffers of stripe_head to share only one real page when page size is bigger than stripe_size. Detail can be seen in patch 8. This patch set is subsequent optimization for configurable stripe_size, which based on the origin patches[1] but reorganized them. Patch 1 is a fixes patch to make sure stripe_size as power of two. Patch 2 try to replace current page offset '0' with dev[i].offset. Patch 3 ~ 7 let xor compute, syndrome and recovery functions support different page offset for raid456. All of these patch are preparing for shared page. There is no functional change. Patch 8 ~ 10 actually implement shared page between multiple devices of stripe_head. But they only make sense for PAGE_SIZE != 4096, likely, 64KB arm64 system. It doesn't make any difference for PAGE_SIZE == 4096 system, likely x86. We have run tests of mdadm for raid456 and test raid6test module. Not found obvious errors. [1] https://www.spinics.net/lists/raid/msg65018.html V2: * Add a fixes patch for stripe_size. * Merge some patch together to avoid building failed. * Pass disks number to init_stripe_shared_pages() rather than using conf->raid_disks, which is not correct on resize_stripes(). Yufen Yu (10): md/raid5: make sure stripe_size as power of two md/raid5: add a new member of offset into r5dev md/raid5: make async_copy_data() to support different page offset md/raid5: add new xor function to support different page offset md/raid5: convert to new xor compution interface md/raid6: let syndrome computor support different page offset md/raid6: let async recovery function support different page offset md/raid5: let multiple devices of stripe_head share page md/raid5: resize stripe_head when reshape array md/raid5: reallocate page array after setting new stripe_size crypto/async_tx/async_pq.c | 72 ++++--- crypto/async_tx/async_raid6_recov.c | 163 +++++++++++----- crypto/async_tx/async_xor.c | 120 ++++++++++-- crypto/async_tx/raid6test.c | 24 ++- drivers/md/raid5.c | 281 ++++++++++++++++++++++++---- drivers/md/raid5.h | 29 ++- include/linux/async_tx.h | 23 ++- 7 files changed, 573 insertions(+), 139 deletions(-) -- 2.25.4
