Li Wang <liwang@xxxxxxxxxx> writes: > 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? > In the next version of the patch I'll add a new test case specifically to test smart scan.
