[LTP] [PATCH v3 2/2] add ksm test for smart-scan feature
Stefan Roesch
shr@devkernel.io
Tue Dec 5 19:01:09 CET 2023
On Tue, Dec 5, 2023, at 5:16 AM, Petr Vorel wrote:
> Hi Stefan,
>
>> This adds a new ksm (kernel samepage merging) test to evaluate the new
>> smart scan feature. It allocates a page and fills it with 'a'
>> characters. It captures the pages_skipped counter, waits for a few
>> iterations and captures the pages_skipped counter again. The expectation
>> is that over 50% of the page scans are skipped (There is only one page
>> that has KSM enabled and it gets scanned during each iteration and it
>> cannot be de-duplicated).
>
>> Signed-off-by: Stefan Roesch <shr@devkernel.io>
>> ---
>> runtest/mm | 1 +
>> testcases/kernel/mem/.gitignore | 1 +
>> testcases/kernel/mem/ksm/ksm07.c | 131 +++++++++++++++++++++++++++++++
>> 3 files changed, 133 insertions(+)
>> create mode 100644 testcases/kernel/mem/ksm/ksm07.c
>
>> diff --git a/runtest/mm b/runtest/mm
>> index f288fed36..d859b331c 100644
>> --- a/runtest/mm
>> +++ b/runtest/mm
>> @@ -70,6 +70,7 @@ ksm05 ksm05 -I 10
>> ksm06 ksm06
>> ksm06_1 ksm06 -n 10
>> ksm06_2 ksm06 -n 8000
>> +ksm07 ksm07
>
>> cpuset01 cpuset01
>
>> diff --git a/testcases/kernel/mem/.gitignore b/testcases/kernel/mem/.gitignore
>> index 7258489ed..c96fe8bfc 100644
>> --- a/testcases/kernel/mem/.gitignore
>> +++ b/testcases/kernel/mem/.gitignore
>> @@ -53,6 +53,7 @@
>> /ksm/ksm04
>> /ksm/ksm05
>> /ksm/ksm06
>> +/ksm/ksm07
>> /mem/mem02
>> /mmapstress/mmap-corruption01
>> /mmapstress/mmapstress01
>> diff --git a/testcases/kernel/mem/ksm/ksm07.c b/testcases/kernel/mem/ksm/ksm07.c
>> new file mode 100644
>> index 000000000..16153fdb2
>> --- /dev/null
>> +++ b/testcases/kernel/mem/ksm/ksm07.c
>> @@ -0,0 +1,131 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * Copyright (C) 2010-2017 Red Hat, Inc.
>> + */
>> +/*\
>> + * [Description]
>> + *
>> + * Kernel Samepage Merging (KSM)
>> + *
>> + * This adds a new ksm (kernel samepage merging) test to evaluate the new
>> + * smart scan feature. It allocates a page and fills it with 'a'
>> + * characters. It captures the pages_skipped counter, waits for a few
>> + * iterations and captures the pages_skipped counter again. The expectation
>> + * is that over 50% of the page scans are skipped (There is only one page
>> + * that has KSM enabled and it gets scanned during each iteration and it
>> + * cannot be de-duplicated).
>> + *
>> + * Prerequisites:
>> + *
>> + * 1) ksm and ksmtuned daemons need to be disabled. Otherwise, it could
>> + * distrub the testing as they also change some ksm tunables depends
>> + * on current workloads.
>> + */
>> +#include <sys/types.h>
>> +#include <sys/mman.h>
>> +#include <sys/stat.h>
>> +#include <sys/wait.h>
>> +#include <errno.h>
>> +#include <fcntl.h>
>> +#include <signal.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <unistd.h>
>> +#include "../include/mem.h"
>> +#include "ksm_common.h"
>> +
>> +/* This test allocates one page, fills the page with a's, captures the
>> + * full_scan and pages_skipped counters. Then it makes sure at least 3
>> + * full scans have been performed and measures the above counters again.
>> + * The expectation is that at least 50% of the pages are skipped.
>> + *
>> + * To wait for at least 3 scans it uses the wait_ksmd_full_scan() function. In
>> + * reality, it will be a lot more scans as the wait_ksmd_full_scan() function
>> + * sleeps for one second.
>> + */
>> +static void create_memory(void)
>> +{
>> + int status;
>> + int full_scans_begin;
>> + int full_scans_end;
>> + int pages_skipped_begin;
>> + int pages_skipped_end;
>> + int diff_pages;
>> + int diff_scans;
>> + unsigned long page_size;
>> + char *memory;
>> +
>> + /* Apply for the space for memory. */
>> + page_size = sysconf(_SC_PAGE_SIZE);
>> + memory = SAFE_MALLOC(page_size);
>> +
>> + for (int i = 0; i < 1; i++) {
>> + memory = SAFE_MMAP(NULL, page_size, PROT_READ|PROT_WRITE,
>> + MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
>> +#ifdef HAVE_DECL_MADV_MERGEABLE
>> + if (madvise(memory, page_size, MADV_MERGEABLE) == -1)
>> + tst_brk(TBROK|TERRNO, "madvise");
>> +#endif
>> + }
>> + memset(memory, 'a', page_size);
>> +
>> + tst_res(TINFO, "KSM merging...");
>> + if (access(PATH_KSM "max_page_sharing", F_OK) == 0) {
>> + SAFE_FILE_PRINTF(PATH_KSM "run", "2");
>> + }
>> +
>> + /* Set defalut ksm scan values. */
>> + SAFE_FILE_PRINTF(PATH_KSM "run", "1");
>> + SAFE_FILE_PRINTF(PATH_KSM "pages_to_scan", "%ld", 100l);
>> + SAFE_FILE_PRINTF(PATH_KSM "sleep_millisecs", "0");
>> +
>> + /* Measure pages skipped aka "smart scan". */
>> + SAFE_FILE_SCANF(PATH_KSM "full_scans", "%d", &full_scans_begin);
>> + SAFE_FILE_SCANF(PATH_KSM "pages_skipped", "%d", &pages_skipped_begin);
> Unfortunately SAFE_FILE_SCANF quits on missing file and
> /sys/kernel/mm/ksm/pages_skipped is not on kernel < 6.7.
>
> safe_file_vprintf() which SAFE_FILE_SCANF() internally uses does not support any
> flag to quit with TCONF instead TBROK when /sys/kernel/mm/ksm/pages_skipped does
> not exists.
>
> We could use access() in setup function, but another line in .save_restore will
> help:
>
> {PATH_KSM "pages_skipped", NULL, TST_SR_TCONF}
>
I don't think this works correctly. I see a warning:
tst_sys_conf.c:144: TINFO: Failed to open FILE '/sys/kernel/mm/ksm/pages_skipped'
The difference to the other ksm files is, that this is not writeable.
>> + wait_ksmd_full_scan();
>> +
>> + tst_res(TINFO, "stop KSM.");
>> + SAFE_FILE_PRINTF(PATH_KSM "run", "0");
>> +
>> + SAFE_FILE_SCANF(PATH_KSM "full_scans", "%d", &full_scans_end);
>> + SAFE_FILE_SCANF(PATH_KSM "pages_skipped", "%d", &pages_skipped_end);
>> + diff_pages = pages_skipped_end - pages_skipped_begin;
>> + diff_scans = full_scans_end - full_scans_begin;
>
> I was going to merge this (with minor cleanup), but the only remaining issue is
> that we allow to test run repeatedly via -iN:
>
> # ./ksm07 -i2
> tst_test.c:1574: TINFO: Timeout per run is 0h 00m 30s
> ksm07.c:73: TINFO: KSM merging...
> ksm_helper.c:36: TINFO: ksm daemon takes 1s to run two full scans
> ksm07.c:88: TINFO: stop KSM.
> ksm07.c:99: TPASS: smart_scan skipped more than 50% of the pages.
> ksm07.c:73: TINFO: KSM merging...
> ksm_helper.c:36: TINFO: ksm daemon takes 1s to run two full scans
> ksm07.c:88: TINFO: stop KSM.
> ksm07.c:97: TFAIL: not enough pages have been skipped by smart_scan.
>
> I'm confused, how to reset KSM to be able to run the test more times?
>
>> +
>> + if (diff_pages < diff_scans * 50 / 100) {
>> + tst_res(TFAIL, "not enough pages have been skipped by smart_scan.");
>> + } else {
>> + tst_res(TPASS, "smart_scan skipped more than 50%% of the pages.");
>> + }
>> +
>> + while (waitpid(-1, &status, 0) > 0)
>> + if (WEXITSTATUS(status) != 0)
>> + tst_res(TFAIL, "child exit status is %d",
>> + WEXITSTATUS(status));
>> +}
> This is not needed, done by check_child_status() in
> lib/tst_test.c.
>
>> +
>> +static void verify_ksm(void)
>> +{
>> + create_memory();
>> +}
> Why this wrapper? "verify_" as a pattern name is not a must.
>> +
>> +static struct tst_test test = {
>> + .needs_root = 1,
>> + .forks_child = 1,
>> + .options = (struct tst_option[]) {
>> + {}
>> + },
>> + .save_restore = (const struct tst_path_val[]) {
>> + {"/sys/kernel/mm/ksm/run", NULL, TST_SR_TCONF},
>> + {"/sys/kernel/mm/ksm/sleep_millisecs", NULL, TST_SR_TCONF},
>> + {"/sys/kernel/mm/ksm/smart_scan", "1",
> We have PATH_KSM definition, lets use it.
>
>> + TST_SR_SKIP_MISSING | TST_SR_TCONF},
>> + {}
>> + },
>> + .needs_kconfigs = (const char *const[]){
>> + "CONFIG_KSM=y",
>> + NULL
>> + },
>> + .test_all = verify_ksm,
>> +};
>
> I was going to merge your patch with following changes.
> We just need solve -i2 issue.
>
I have a solution for this: we need another madvise call at the end. I'll send
it with the next version.
> Kind regards,
> Petr
>
> diff --git testcases/kernel/mem/ksm/ksm07.c testcases/kernel/mem/ksm/ksm07.c
> index 16153fdb2..e5c31775b 100644
> --- testcases/kernel/mem/ksm/ksm07.c
> +++ testcases/kernel/mem/ksm/ksm07.c
> @@ -5,35 +5,25 @@
> /*\
> * [Description]
> *
> - * Kernel Samepage Merging (KSM)
> + * Kernel Samepage Merging (KSM) for smart scan feature
> *
> - * This adds a new ksm (kernel samepage merging) test to evaluate the new
> - * smart scan feature. It allocates a page and fills it with 'a'
> - * characters. It captures the pages_skipped counter, waits for a few
> - * iterations and captures the pages_skipped counter again. The expectation
> - * is that over 50% of the page scans are skipped (There is only one page
> - * that has KSM enabled and it gets scanned during each iteration and it
> - * cannot be de-duplicated).
> + * Test allocates a page and fills it with 'a' characters. It captures the
> + * pages_skipped counter, waits for a few iterations and captures the
> + * pages_skipped counter again. The expectation is that over 50% of the page
> + * scans are skipped. (There is only one page that has KSM enabled and it gets
> + * scanned during each iteration and it cannot be de-duplicated.)
> *
> - * Prerequisites:
> + * Smart scan feature was added in kernel v6.7.
> *
> - * 1) ksm and ksmtuned daemons need to be disabled. Otherwise, it could
> - * distrub the testing as they also change some ksm tunables depends
> - * on current workloads.
> + * [Prerequisites]
> + *
> + * ksm and ksmtuned daemons need to be disabled. Otherwise, it could
> + * distrub the testing as they also change some ksm tunables depends
> + * on current workloads.
> */
> -#include <sys/types.h>
> -#include <sys/mman.h>
> -#include <sys/stat.h>
> +
> #include <sys/wait.h>
> -#include <errno.h>
> -#include <fcntl.h>
> -#include <signal.h>
> -#include <stdio.h>
> -#include <stdlib.h>
> -#include <string.h>
> -#include <unistd.h>
> -#include "../include/mem.h"
> -#include "ksm_common.h"
> +#include "mem.h"
>
> /* This test allocates one page, fills the page with a's, captures the
> * full_scan and pages_skipped counters. Then it makes sure at least 3
> @@ -46,7 +36,6 @@
> */
> static void create_memory(void)
> {
> - int status;
> int full_scans_begin;
> int full_scans_end;
> int pages_skipped_begin;
> @@ -70,10 +59,10 @@ static void create_memory(void)
> }
> memset(memory, 'a', page_size);
>
> - tst_res(TINFO, "KSM merging...");
> - if (access(PATH_KSM "max_page_sharing", F_OK) == 0) {
> + tst_res(TINFO, "KSM merging");
> +
> + if (access(PATH_KSM "max_page_sharing", F_OK) == 0)
> SAFE_FILE_PRINTF(PATH_KSM "run", "2");
> - }
>
> /* Set defalut ksm scan values. */
> SAFE_FILE_PRINTF(PATH_KSM "run", "1");
> @@ -85,7 +74,7 @@ static void create_memory(void)
> SAFE_FILE_SCANF(PATH_KSM "pages_skipped", "%d", &pages_skipped_begin);
> wait_ksmd_full_scan();
>
> - tst_res(TINFO, "stop KSM.");
> + tst_res(TINFO, "stop KSM");
> SAFE_FILE_PRINTF(PATH_KSM "run", "0");
>
> SAFE_FILE_SCANF(PATH_KSM "full_scans", "%d", &full_scans_end);
> @@ -93,21 +82,10 @@ static void create_memory(void)
> diff_pages = pages_skipped_end - pages_skipped_begin;
> diff_scans = full_scans_end - full_scans_begin;
>
> - if (diff_pages < diff_scans * 50 / 100) {
> - tst_res(TFAIL, "not enough pages have been skipped by smart_scan.");
> - } else {
> - tst_res(TPASS, "smart_scan skipped more than 50%% of the pages.");
> - }
> -
> - while (waitpid(-1, &status, 0) > 0)
> - if (WEXITSTATUS(status) != 0)
> - tst_res(TFAIL, "child exit status is %d",
> - WEXITSTATUS(status));
> -}
> -
> -static void verify_ksm(void)
> -{
> - create_memory();
> + if (diff_pages < diff_scans * 50 / 100)
> + tst_res(TFAIL, "not enough pages have been skipped by smart_scan");
> + else
> + tst_res(TPASS, "smart_scan skipped more than 50%% of the pages");
> }
>
> static struct tst_test test = {
> @@ -117,9 +95,10 @@ static struct tst_test test = {
> {}
> },
> .save_restore = (const struct tst_path_val[]) {
> - {"/sys/kernel/mm/ksm/run", NULL, TST_SR_TCONF},
> - {"/sys/kernel/mm/ksm/sleep_millisecs", NULL, TST_SR_TCONF},
> - {"/sys/kernel/mm/ksm/smart_scan", "1",
> + {PATH_KSM "pages_skipped", NULL, TST_SR_TCONF},
> + {PATH_KSM "run", NULL, TST_SR_TCONF},
> + {PATH_KSM "sleep_millisecs", NULL, TST_SR_TCONF},
> + {PATH_KSM "smart_scan", "1",
> TST_SR_SKIP_MISSING | TST_SR_TCONF},
> {}
> },
> @@ -127,5 +106,5 @@ static struct tst_test test = {
> "CONFIG_KSM=y",
> NULL
> },
> - .test_all = verify_ksm,
> + .test_all = create_memory,
> };
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