From: Pankaj Raghav <p.raghav@samsung.com>

Add block size > page size to ramfs as we support minimum folio order
allocation in the page cache. The changes are very minimal, and this is
also a nice way to stress test just the page cache changes for minimum
folio order.

I tested the changes from blocksize 4k to 2M with ltp's fsx on an x86
machine.

I ran a basic perf test with dd as follows:
$ mount ramfs -t ramfs -o blocksize=$bs /media/test/
$ dd if=/mnt/rand of="/media/test/rand" bs=2M count=2048

+------+----------+
|  bs  | BW(GB/s) |
+------+----------+
| 4k   |      1.7 |
| 8k   |      2.4 |
| 16k  |      3.2 |
| 32k  |      4.0 |
| 64k  |      4.5 |
| 128k |      4.8 |
| 256k |      5.3 |
| 512k |      5.5 |
| 1M   |      5.6 |
| 2M   |      5.6 |
+------+----------+

We get better performance for larger bs as we allocate larger folios
instead of multiple smaller folios when there is no memory fragmentation
and pressure.

Pankaj Raghav (2):
  ramfs: add blocksize mount option
  ramfs: enable block size > page size

 fs/ramfs/inode.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)


base-commit: 4d0326b60bb753627437fff0f76bf1525bcda422
-- 
2.44.1

On Tue, Sep 24, 2024 at 09:23:49PM +0200, Pankaj Raghav (Samsung) wrote:
> Add block size > page size to ramfs as we support minimum folio order
> allocation in the page cache. The changes are very minimal, and this is
> also a nice way to stress test just the page cache changes for minimum
> folio order.

I don't really see the point of upstreaming this.  I'm sure it was
useful for your testing.  And splitting the patch in two makes no sense
to me; the combined patch is not large.

> Pankaj Raghav (2):
>   ramfs: add blocksize mount option
>   ramfs: enable block size > page size
> 
>  fs/ramfs/inode.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)

On Tue, Sep 24, 2024 at 09:00:26PM +0100, Matthew Wilcox wrote:
> On Tue, Sep 24, 2024 at 09:23:49PM +0200, Pankaj Raghav (Samsung) wrote:
> > Add block size > page size to ramfs as we support minimum folio order
> > allocation in the page cache. The changes are very minimal, and this is
> > also a nice way to stress test just the page cache changes for minimum
> > folio order.
>
> I don't really see the point of upstreaming this.  I'm sure it was
> useful for your testing.  And splitting the patch in two makes no sense
> to me; the combined patch is not large.

I just wanted to put it out in the wild to see if somebody found it
useful as it was pretty trivial to add the support. Also, the first
series that tried adding support for LBS in the kernel 17 years ago used
ramfs as an example :).

The only use case I could come up with was testing the folio order changes
in the page cache without having to use a more complicated FS like XFS.
In that sense it is still useful to add this feature I guess considering
the minimal changes?

--
Pankaj