While building kernel documention using make htmldocs command, I was
getting unexpected indentation error. Single description was given for
two module parameters with wrong indentation. So, I corrected the
indentation of both parameters and the description.

Signed-off-by: Shibu kumar <shibukumar.bit@gmail.com>
Signed-off-by: Daniel Yang <danielyangkang@gmail.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: 0d815e3400e6 ("dm-crypt: limit the size of encryption requests")

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

There was a performance regression reported where dm-crypt would perform
worse on new kernels than on old kernels. The reason is that the old
kernels split the bios to NVMe request size (that is usually 65536 or
131072 bytes) and the new kernels pass the big bios through dm-crypt and
split them underneath.

If a big 1MiB bio is passed to dm-crypt, dm-crypt processes it on a single
core without parallelization and this is what causes the performance
degradation.

This commit introduces new tunable variables
/sys/module/dm_crypt/parameters/max_read_size and
/sys/module/dm_crypt/parameters/max_write_size that specify the maximum
bio size for dm-crypt. Bios larger than this value are split, so that
they can be encrypted in parallel by multiple cores. If these variables
are '0', a default 131072 is used.

Splitting bios may cause performance regressions in other workloads - if
this happens, the user should increase the value in max_read_size and
max_write_size variables.

max_read_size:
128k    2399MiB/s
256k    2368MiB/s
512k    1986MiB/s
1024    1790MiB/s

max_write_size:
128k    1712MiB/s
256k    1651MiB/s
512k    1537MiB/s
1024k   1332MiB/s

Note that if you run dm-crypt inside a virtual machine, you may need to do
"echo numa >/sys/module/workqueue/parameters/default_affinity_scope" to
improve performance.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>

When WQ_HIGHPRI was used for the dm-crypt kcryptd workqueue it was
reported that dm-crypt performs badly when the system is loaded[1].
Because of reports of audio skipping, dm-crypt stopped using
WQ_HIGHPRI with commit f612b2132db5 (Revert "dm crypt: use WQ_HIGHPRI
for the IO and crypt workqueues").

But it has since been determined that WQ_HIGHPRI provides improved
performance (with reduced latency) for highend systems with much more
resources than those laptop/desktop users which suffered from the use
of WQ_HIGHPRI.

As such, add an option "high_priority" that allows the use of
WQ_HIGHPRI for dm-crypt's workqueues and also sets the write_thread to
nice level MIN_NICE (-20). This commit makes it optional, so that
normal users won't be harmed by it.

[1] https://listman.redhat.com/archives/dm-devel/2023-February/053410.html

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Signed-off-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Add more documentation details for most aspects of the data_vio
read and write processes. Also correct a few minor errors and
rewrite some text for clarity.

Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

This adds the admin-guide documentation for dm-vdo.

vdo.rst is the guide to using dm-vdo. vdo-design is an overview of the
design of dm-vdo.

Co-developed-by: J. corwin Coburn <corwin@hurlbutnet.net>
Signed-off-by: J. corwin Coburn <corwin@hurlbutnet.net>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Signed-off-by: Russell Harmon <eatnumber1@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>