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Message-ID: <fe6362b2-c399-7d51-b0e4-15e6ed445767@suse.cz>
Date: Thu, 16 Jun 2022 10:23:14 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Jakub Matěna <matenajakub@...il.com>,
akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, patches@...ts.linux.dev,
linux-kernel@...r.kernel.org, mhocko@...nel.org,
mgorman@...hsingularity.net, willy@...radead.org,
liam.howlett@...cle.com, hughd@...gle.com, kirill@...temov.name,
riel@...riel.com, rostedt@...dmis.org, peterz@...radead.org
Subject: Re: [PATCH v4 2/2] [PATCH 2/2] mm: add merging after mremap resize
On 6/3/22 16:57, Jakub Matěna wrote:
> When mremap call results in expansion, it might be possible to merge the
> VMA with the next VMA which might become adjacent. This patch adds
> vma_merge call after the expansion is done to try and merge.
>
> Signed-off-by: Jakub Matěna <matenajakub@...il.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> mm/mremap.c | 19 +++++++++-
> tools/testing/selftests/vm/mremap_test.c | 47 +++++++++++++++++++++++-
> 2 files changed, 63 insertions(+), 3 deletions(-)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 0b93fac76851..66970dcd636a 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -9,6 +9,7 @@
> */
>
> #include <linux/mm.h>
> +#include <linux/mm_inline.h>
> #include <linux/hugetlb.h>
> #include <linux/shm.h>
> #include <linux/ksm.h>
> @@ -23,6 +24,7 @@
> #include <linux/mmu_notifier.h>
> #include <linux/uaccess.h>
> #include <linux/userfaultfd_k.h>
> +#include <linux/mempolicy.h>
>
> #include <asm/cacheflush.h>
> #include <asm/tlb.h>
> @@ -1014,6 +1016,9 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> /* can we just expand the current mapping? */
> if (vma_expandable(vma, new_len - old_len)) {
> long pages = (new_len - old_len) >> PAGE_SHIFT;
> + unsigned long extension_start = addr + old_len;
> + unsigned long extension_end = addr + new_len;
> + pgoff_t extension_pgoff = vma->vm_pgoff + (old_len >> PAGE_SHIFT);
>
> if (vma->vm_flags & VM_ACCOUNT) {
> if (security_vm_enough_memory_mm(mm, pages)) {
> @@ -1022,8 +1027,18 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> }
> }
>
> - if (vma_adjust(vma, vma->vm_start, addr + new_len,
> - vma->vm_pgoff, NULL)) {
> + /*
> + * Function vma_merge() is called on the extension we are adding to
> + * the already existing vma, vma_merge() will merge this extension with
> + * the already existing vma (expand operation itself) and possibly also
> + * with the next vma if it becomes adjacent to the expanded vma and
> + * otherwise compatible.
> + */
> + vma = vma_merge(mm, vma, extension_start, extension_end,
> + vma->vm_flags, vma->anon_vma, vma->vm_file,
> + extension_pgoff, vma_policy(vma),
> + vma->vm_userfaultfd_ctx, anon_vma_name(vma));
> + if (!vma) {
> vm_unacct_memory(pages);
> ret = -ENOMEM;
> goto out;
> diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
> index db0270127aeb..0865a6cb5bdb 100644
> --- a/tools/testing/selftests/vm/mremap_test.c
> +++ b/tools/testing/selftests/vm/mremap_test.c
> @@ -118,6 +118,48 @@ static unsigned long long get_mmap_min_addr(void)
> return addr;
> }
>
> +/*
> + * This test validates that merge is called when expanding a mapping.
> + * Mapping containing three pages is created, middle page is unmapped
> + * and then the mapping containing the first page is expanded so that
> + * it fills the created hole. The two parts should merge creating
> + * single mapping with three pages.
> + */
> +static void mremap_expand_merge(unsigned long page_size)
> +{
> + char *test_name = "mremap expand merge";
> + FILE *fp;
> + char *line = NULL;
> + size_t len = 0;
> + bool success = false;
> +
> + char *start = mmap(NULL, 3 * page_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> + munmap(start + page_size, page_size);
> + mremap(start, page_size, 2 * page_size, 0);
> +
> + fp = fopen("/proc/self/maps", "r");
> + if (fp == NULL) {
> + ksft_test_result_fail("%s\n", test_name);
> + return;
> + }
> +
> + while(getline(&line, &len, fp) != -1) {
> + char *first = strtok(line,"- ");
> + void *first_val = (void *) strtol(first, NULL, 16);
> + char *second = strtok(NULL,"- ");
> + void *second_val = (void *) strtol(second, NULL, 16);
> + if (first_val == start && second_val == start + 3 * page_size) {
> + success = true;
> + break;
> + }
> + }
> + if (success)
> + ksft_test_result_pass("%s\n", test_name);
> + else
> + ksft_test_result_fail("%s\n", test_name);
> + fclose(fp);
> +}
> +
> /*
> * Returns the start address of the mapping on success, else returns
> * NULL on failure.
> @@ -336,6 +378,7 @@ int main(int argc, char **argv)
> int i, run_perf_tests;
> unsigned int threshold_mb = VALIDATION_DEFAULT_THRESHOLD;
> unsigned int pattern_seed;
> + int num_expand_tests = 1;
> struct test test_cases[MAX_TEST];
> struct test perf_test_cases[MAX_PERF_TEST];
> int page_size;
> @@ -407,12 +450,14 @@ int main(int argc, char **argv)
> (threshold_mb * _1MB >= _1GB);
>
> ksft_set_plan(ARRAY_SIZE(test_cases) + (run_perf_tests ?
> - ARRAY_SIZE(perf_test_cases) : 0));
> + ARRAY_SIZE(perf_test_cases) : 0) + num_expand_tests);
>
> for (i = 0; i < ARRAY_SIZE(test_cases); i++)
> run_mremap_test_case(test_cases[i], &failures, threshold_mb,
> pattern_seed);
>
> + mremap_expand_merge(page_size);
> +
> if (run_perf_tests) {
> ksft_print_msg("\n%s\n",
> "mremap HAVE_MOVE_PMD/PUD optimization time comparison for 1GB region:");
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