[RFC 0/4] minimum folio order support in filemap

[Pankaj Raghav]

There has been a lot of discussion recently to support devices and fs for
bs > ps. One of the main plumbing to support buffered IO is to have a minimum
order while allocating folios in the page cache.

Hannes sent recently a series[1] where he deduces the minimum folio
order based on the i_blkbits in struct inode. This takes a different
approach based on the discussion in that thread where the minimum and
maximum folio order can be set individually per inode.

This series is based on top of Christoph's patches to have iomap aops
for the block cache[2]. I rebased his remaining patches to
next-20230621. The whole tree can be found here[3].

Compiling the tree with CONFIG_BUFFER_HEAD=n, I am able to do a buffered
IO on a nvme drive with bs>ps in QEMU without any issues:

[root@archlinux ~]# cat /sys/block/nvme0n2/queue/logical_block_size
16384
[root@archlinux ~]# fio -bs=16k -iodepth=8 -rw=write -ioengine=io_uring -size=500M
		    -name=io_uring_1 -filename=/dev/nvme0n2 -verify=md5
io_uring_1: (g=0): rw=write, bs=(R) 16.0KiB-16.0KiB, (W) 16.0KiB-16.0KiB, (T) 16.0KiB-16.0KiB, ioengine=io_uring, iodepth=8
fio-3.34
Starting 1 process
Jobs: 1 (f=1): [V(1)][100.0%][r=336MiB/s][r=21.5k IOPS][eta 00m:00s]
io_uring_1: (groupid=0, jobs=1): err= 0: pid=285: Wed Jun 21 07:58:29 2023
  read: IOPS=27.3k, BW=426MiB/s (447MB/s)(500MiB/1174msec)
  <snip>
Run status group 0 (all jobs):
   READ: bw=426MiB/s (447MB/s), 426MiB/s-426MiB/s (447MB/s-447MB/s), io=500MiB (524MB), run=1174-1174msec
  WRITE: bw=198MiB/s (207MB/s), 198MiB/s-198MiB/s (207MB/s-207MB/s), io=500MiB (524MB), run=2527-2527msec

Disk stats (read/write):
  nvme0n2: ios=35614/4297, merge=0/0, ticks=11283/1441, in_queue=12725, util=96.27%

One of the main dependency to work on a block device with bs>ps is
Christoph's work on converting block device aops to use iomap.

[1] https://lwn.net/Articles/934651/
[2] https://lwn.net/ml/linux-kernel/20230424054926.26927-1-hch@xxxxxx/
[3] https://github.com/Panky-codes/linux/tree/next-20230523-filemap-order-generic-v1

Luis Chamberlain (1):
  block: set mapping order for the block cache in set_init_blocksize

Matthew Wilcox (Oracle) (1):
  fs: Allow fine-grained control of folio sizes

Pankaj Raghav (2):
  filemap: use minimum order while allocating folios
  nvme: enable logical block size > PAGE_SIZE

 block/bdev.c             |  9 ++++++++
 drivers/nvme/host/core.c |  2 +-
 include/linux/pagemap.h  | 46 ++++++++++++++++++++++++++++++++++++----
 mm/filemap.c             |  9 +++++---
 mm/readahead.c           | 34 ++++++++++++++++++++---------
 5 files changed, 82 insertions(+), 18 deletions(-)

-- 
2.39.2