Re: [PATCH 2/2] selftests/mm: add test for vrealloc() shrink page freeing

[Jill Ravaliya]

Hey Uladzislau,

Thanks for pointing that out. I'll check test_vmalloc.c right away.

Jill

On Sat, May 23, 2026 at 9:50 PM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
>
> On Thu, May 07, 2026 at 05:18:54PM +0530, Jill Ravaliya wrote:
> > Add a selftest that verifies vrealloc() frees physical pages
> > when shrinking an allocation.
> >
> > The test loads a kernel module that:
> > 1. Allocates 10MB with vmalloc()
> > 2. Touches all pages to force physical allocation
> > 3. Shrinks to 2MB with vrealloc()
> > 4. Verifies free page count increased after shrink
> >
> > Without the fix, the test fails because no pages are freed.
> > With the fix applied, the test passes confirming ~2048 pages
> > are returned to the system after shrinking from 10MB to 2MB.
> >
> > Tested on kernel 7.0.0 in QEMU.
> >
> > Signed-off-by: Jill Ravaliya <jillravaliya@xxxxxxxxx>
> > ---
> >  tools/testing/selftests/mm/Makefile           |  5 ++
> >  .../selftests/mm/vrealloc_shrink_test.c       | 65 +++++++++++++++++++
> >  2 files changed, 70 insertions(+)
> >  create mode 100644 tools/testing/selftests/mm/vrealloc_shrink_test.c
> >
> > diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> > index cd24596cd..4eab7c76c 100644
> > --- a/tools/testing/selftests/mm/Makefile
> > +++ b/tools/testing/selftests/mm/Makefile
> > @@ -104,6 +104,7 @@ TEST_GEN_FILES += hugetlb_dio
> >  TEST_GEN_FILES += droppable
> >  TEST_GEN_FILES += guard-regions
> >  TEST_GEN_FILES += merge
> > +TEST_GEN_FILES += vrealloc_shrink_test
> >  TEST_GEN_FILES += rmap
> >  TEST_GEN_FILES += folio_split_race_test
> >
> > @@ -282,3 +283,7 @@ warn_missing_page_frag:
> >       echo "Warning: $(PAGE_FRAG_WARNING). page_frag test will be skipped." ; \
> >       echo
> >  endif
> > +
> > +# vrealloc shrink test module
> > +vrealloc_shrink_mod.ko: vrealloc_shrink_mod.c
> > +     $(MAKE) -C $(KDIR) M=$(PWD) modules
> > diff --git a/tools/testing/selftests/mm/vrealloc_shrink_test.c b/tools/testing/selftests/mm/vrealloc_shrink_test.c
> > new file mode 100644
> > index 000000000..cf4263074
> > --- /dev/null
> > +++ b/tools/testing/selftests/mm/vrealloc_shrink_test.c
> > @@ -0,0 +1,65 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Test that vrealloc() frees physical pages when shrinking.
> > + *
> > + * vrealloc() shrink path previously zeroed unused memory and updated
> > + * vm->requested_size, but never freed the physical pages backing the
> > + * unused portion of the allocation. This test verifies the fix by
> > + * loading a kernel module that directly measures nr_pages before and
> > + * after vrealloc() shrink.
> > + *
> > + * Copyright (C) 2026 Jill Ravaliya
> > + */
> > +
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <unistd.h>
> > +#include <fcntl.h>
> > +#include "../kselftest.h"
> > +
> > +#define MODULE_NAME "vrealloc_shrink_mod"
> > +#define DMESG_PASS  "vrealloc_shrink: PASS"
> > +#define DMESG_FAIL  "vrealloc_shrink: FAIL"
> > +
> > +static int run_cmd(const char *cmd)
> > +{
> > +     return system(cmd);
> > +}
> > +
> > +static int check_dmesg_for(const char *pattern)
> > +{
> > +     char cmd[256];
> > +     snprintf(cmd, sizeof(cmd),
> > +              "dmesg | grep -q '%s'", pattern);
> > +     return system(cmd) == 0;
> > +}
> > +
> > +int main(void)
> > +{
> > +     ksft_print_header();
> > +     ksft_set_plan(1);
> > +
> > +     /* Insert the test module */
> > +     if (run_cmd("insmod " MODULE_NAME ".ko") != 0) {
> > +             ksft_test_result_skip(
> > +                     "could not load %s.ko - is it built?\n",
> > +                     MODULE_NAME);
> > +             ksft_finished();
> > +     }
> > +
> > +     /* Check dmesg for pass/fail */
> > +     if (check_dmesg_for(DMESG_PASS)) {
> > +             ksft_test_result_pass(
> > +                     "vrealloc shrink frees physical pages\n");
> > +     } else if (check_dmesg_for(DMESG_FAIL)) {
> > +             ksft_test_result_fail(
> > +                     "vrealloc shrink did NOT free physical pages\n");
> > +     } else {
> > +             ksft_test_result_fail(
> > +                     "could not find test result in dmesg\n");
> > +     }
> > +
> > +     run_cmd("rmmod " MODULE_NAME);
> > +     ksft_finished();
> > +}
> > --
> > 2.43.0
> >
> We have a test case that covers vrealloc() functionality. See test_vmalloc.c
> file.
>
> --
> Uladzislau Rezki