[PATCH 0/2] improve buffered write performance with fgf order hint

[Pankaj Raghav (Samsung)]

From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>

Filesystems that support large folios can set the fgf order before
buffered write(see XFS iomap_write_begin()) that can provide as a hint
to page cache to allocate large folios, if possible.

The first patch is a minor cleanup.
The second patch sets fgf order before starting the buffered write.

I tested the performance on Samsung SSD 990 pro on a system with 64GB
RAM as follows:

$ bcachefs format -f /dev/nvme0n1;
$ mount -t bcachefs /dev/nvme0n1 /mnt
$ fio --name=bcachefs --filename=/mnt/test  --size=100G \
    --ioengine=io_uring --iodepth=16 --rw=write --bs=128k

I measured the BW(MB/s) across three runs on 6.10-rc3:
Before patches: 2730
After patches: 3430 (1.25x boost)

With -o no_data_io mount option:
Before patches: 2920
After patches: 4630 (1.5x boost)

I was not able to test the patches with ktest due to some issue with
debian(some broken package issue). Maybe Kent can run it in his CI while
I try to fix ktest locally?

Pankaj Raghav (2):
  bcachefs: use FGP_WRITEBEGIN instead of combining individual flags
  bcachefs: set fgf order hint before starting a buffered write

 fs/bcachefs/fs-io-buffered.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)


base-commit: 03d44168cbd7fc57d5de56a3730427db758fc7f6
-- 
2.44.1