Hi Stefan, Petr,
On Tue, Nov 28, 2023 at 3:46 PM Petr Vorel <pvorel@xxxxxxx> wrote:
Hi Stefan,
> This disables the "smart scan" KSM feature to make sure that the volatile
> count remains at 0.
> Signed-off-by: Stefan Roesch <devkernel.io>
nit: you forgot 'shr@'
Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx>
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202311161132.13d8ce5a-oliver.sang@xxxxxxxxx
> ---
> testcases/kernel/mem/lib/mem.c | 4 ++++
> 1 file changed, 4 insertions(+)
> diff --git a/testcases/kernel/mem/lib/mem.c b/testcases/kernel/mem/lib/mem.c
> index fbfeef026..ef274a3ac 100644
> --- a/testcases/kernel/mem/lib/mem.c
> +++ b/testcases/kernel/mem/lib/mem.c
> @@ -454,6 +454,9 @@ void create_same_memory(int size, int num, int unit)
> {'a', size*MB}, {'a', size*MB}, {'d', size*MB}, {'d', size*MB},
> };
> + /* Disable smart scan for correct volatile counts. */
> + SAFE_FILE_PRINTF(PATH_KSM "smart_scan", "0");
NOTE, this fails on the systems without /sys/kernel/mm/ksm/smart_scan:
mem.c:458: TBROK: Failed to open FILE '/sys/kernel/mm/ksm/smart_scan' for writing: EACCES (13)
NOTE, we normally handle the setup like this in test setup function.
But new API has .save_restore which is more robust for tasks like this.
It's already used in ksm01.c, you need just to add this line:
{"/sys/kernel/mm/ksm/smart_scan", "0", TST_SR_SKIP},
I guess we need to set 'TST_SR_SKIP_MISSING | TST_SR_TBROK_RO'
as the last field. Because TST_SR_SKIP will continue the test without
writing '0' to the smart_scan file, that's not correct if the file exists. It will
ignore a kernel bug (smart_scan can't be written) by that config.
Per the Doc Petr pointed below:
TST_SR_SKIP_MISSING – Continue without saving the file if it does not exist TST_SR_TBROK_RO – End test with TBROK if the file is read-only
TST_SR_SKIP_RO – Continue without saving the file if it is read-only
TST_SR_SKIP – Equivalent to 'TST_SR_SKIP_MISSING | TST_SR_SKIP_RO'
(instead of both SAFE_FILE_PRINTF)
See:
https://github.com/linux-test-project/ltp/wiki/C-Test-API#127-saving--restoring-procsys-values
I wonder if ksm01.c is the only ksm test which needs to disable this.
I think all of the ksm0*.c tests should disable it by the config. The smart_scan
will impact all the tests with invoke key function create_same_memory().
also nit: there is a wrong indent (spaces instead of tabs), please be consistent
with the file content.
NOTE: while this fixes problem on 6.7.0-rc1-2.g86e46c2-default (openSUSE),
it does not fixes other problem on 6.5.10 on Debian (16 errors like these below):
mem.c:252: TFAIL: pages_shared is not 2 but 5038.
mem.c:252: TFAIL: pages_sharing is not 98302 but 593629.
mem.c:252: TFAIL: pages_volatile is not 0 but 391.
mem.c:252: TFAIL: pages_unshared is not 0 but 149157.
I have no idea if this is a real bug which needs to be fixed or test false
positive to be fixed, or whether the problem has already been fixed in newer
kernels.
It is more like a real bug, the Debain kernel-6.5.10 does not contain
this smart_scan feature. Or you may try to build the latest kernel
on your platform to see if it can be reproduced as well.
> +
> ps = sysconf(_SC_PAGE_SIZE);
> pages = MB / ps;
> @@ -526,6 +529,7 @@ void create_same_memory(int size, int num, int unit)
> tst_res(TINFO, "stop KSM.");
> SAFE_FILE_PRINTF(PATH_KSM "run", "0");
> + SAFE_FILE_PRINTF(PATH_KSM "smart_scan", "1");
nit: Again, wrong indent. You could have seen it also in the generated patch.
Kind regards,
Petr
> final_group_check(0, 0, 0, 0, 0, 0, size * pages * num);
> while (waitpid(-1, &status, 0) > 0)
> base-commit: 8c89ef3d451087ed6e18750bd5eedd10e5ab3d2e
One more comment not related to this patch:
@Stefan, do you have a test (or plan to) verify the 'smart_scan' feture works?
As we do disables it for all ksm* tests in LTP, so, it would be great to have one
for testing in enable mode. What do you think?
Regards,
Li Wang
