Gentle ping Minchan and Sergey. Regards, Pankaj On 2023-09-11 15:34, Pankaj Raghav wrote: > ZRAM can have a backing device that could be used as a writeback device > for the pages in RAM. The current writeback code (writeback_store()) does > a synchronous single page size IO to the backing device. > > This series implements IO batching while doing a writeback to a backing > device. The code still does synchronous IOs but with larger IO sizes > whenever possible. This crosses off one of the TODO that was there as a part > of writeback_store() function: > A single page IO would be inefficient for write... > > The idea is to batch the IOs to a certain limit before the data is flushed > to the backing device. The batch limit is initially chosen based on the > bdi->io_pages value with an upper limit of 32 pages (128k on x86). > > Batching reduces the time of writeback of 4G data to a nvme backing device > from 68 secs to 15 secs (more than **4x improvement**). > > The first 3 patches are prep. 4th patch implements the main logic for IO > batching and the last patch is another cleanup. > > Perf: > > $ modprobe zram num_devices=1 > $ echo "/dev/nvme0n1" > /sys/block/zram0/backing_dev > $ echo 6G > /sys/block/zram0/disksize > $ fio -iodepth=16 -rw=randwrite -ioengine=io_uring -bs=4k -numjobs=1 -size=4G -filename=/dev/zram0 -name=io_uring_1 > /dev/null > $ echo all > /sys/block/zram0/idle > > Without changes: > $ time echo idle > /sys/block/zram0/writeback > real 1m8.648s (68 secs) > user 0m0.000s > sys 0m24.899s > $ cat /sys/block/zram0/bd_stat > 1048576 0 1048576 > > With changes: > $ time echo idle > /sys/block/zram0/writeback > real 0m15.496s (15 secs) > user 0m0.000s > sys 0m7.789s > $ cat /sys/block/zram0/bd_stat > 1048576 0 1048576 > > Testing: > > A basic End-End testing (based on Sergey's test flow [1]): > 1) configure zram0 and add a nvme device as a writeback device > 2) Get the sha256sum of a tarball > 3) mkfs.ext4 on zram0, cp tarball > 4) idle writeback > 5) cp tarball from zram0 to another device (reread writeback pages) and > compare the sha256sum again > The sha before and after are verified to be the same. > > Writeback limit testing: > > 1) configure zram0 and add a nvme device as a writeback device > 2) Set writeback limit and enable > 3) Do a fio that crosses the writeback limit > 4) idle writeback > 5) Verify the writeback is limited to the set writeback limit value > > $ modprobe zram num_devices=1 > $ echo "/dev/nvme0n1" > /sys/block/zram0/backing_dev > $ echo 4G > /sys/block/zram0/disksize > $ echo 1 > /sys/block/zram0/writeback_limit_enable > $ echo 1002 > /sys/block/zram0/writeback_limit > > $ fio -iodepth=16 -rw=write -ioengine=io_uring -bs=4k -numjobs=1 -size=10M -filename=/dev/zram0 -name=io_uring_1 > > $ echo all > /sys/block/zram0/idle > $ echo idle > /sys/block/zram0/writeback > $ cat /sys/block/zram0/bd_stat > 1002 0 1002 > > writeback is limited to the set value. > > [1] https://lore.kernel.org/lkml/20230806071601.GB907732@xxxxxxxxxx/ > > Pankaj Raghav (5): > zram: move index preparation to a separate function in writeback_store > zram: encapsulate writeback to the backing bdev in a function > zram: add alloc_block_bdev_range() and free_block_bdev_range() > zram: batch IOs during writeback to improve performance > zram: don't overload blk_idx variable in writeback_store() > > drivers/block/zram/zram_drv.c | 318 ++++++++++++++++++++++------------ > 1 file changed, 210 insertions(+), 108 deletions(-) > > > base-commit: 7bc675554773f09d88101bf1ccfc8537dc7c0be9
