Re: [PATCH RFC] fat: use write_inode_now() on flush to avoid racing the flusher

[Bryanna Marihugh]

On 10/29/26 2:56 PM, OGAWA Hirofumi wrote:
> Looks like this waits the I/O, and sounds like optimization only for
> specific drives. Well, so no slowdown for other drives by this patch?

Thanks for the rapid reply and feedback.

writeback_inode is called only when flush is set. My understanding is
that mode is for storage that could disconnect. I set write_inode_now
to wait as that seemed to be right for flush. Given it does change
behavior I should have explained that better. I can change it to 0 if
you want the old behavior. Because I_SYNC is still set no matter if
it waits or not, it should keep the kernel flusher from writing the
same file.

I focused on the reduced write request size causing the stall, and
tested for slowdowns mostly doing a cp and looking at the times, for
big and small files. Everything in MB/s

PNY 32G stick (usb-storage), copying a 3 GiB file 3x

  before: 16.3, 13.2, 11.6
  after:  18.0, 18.0, 17.6

Samsung 64G stick (usb-storage), copying a 3 GiB file 3x

  before: 33.4, 33.5, 33.5
  after:  33.5, 33.5, 33.5

PNY 250G stick (uas), copying a 4 GiB file 3x

  before: 365, 200, 322
  after:  365, 255, 251

Samsung 870 EVO in a USB-SATA adapter (uas), copying a 4 GiB file 3x

  before: 379, 346, 346
  after:  376, 378, 379

The PNY 250G numbers vary on both kernels because the stick slows
itself down partway through.

For small files I saw maybe improvements on the cheap stick, with no
harm on the nicer Samsung stick.

PNY 32G stick (usb-storage), copying 1000 x 1 MiB files 2x

  before: 5.37, 5.55
  after:  5.64, 5.62

Samsung 64G stick (usb-storage), copying 1000 x 1 MiB files 2x

  before: 7.33, 7.37
  after:  7.35, 7.36

PNY 250G stick (uas), copying 1000 x 1 MiB files 2x

  before: 9.61, 9.61
  after:  9.28, 9.26

870 EVO in USB-SATA adapter (uas), copying 1000 x 1 MiB files 2x

  before: 9.61, 9.61
  after:  9.59, 9.51

There is some regression with small files on the uas drives from the
wait.

Thanks,
Bryanna