On 19 Mar 2021, at 19:37, Yang Shi wrote:
On Thu, Mar 18, 2021 at 5:52 PM Zi Yan zi.yan@sent.com wrote:
From: Zi Yan ziy@nvidia.com
We did not have a direct user interface of splitting the compound page backing a THP and there is no need unless we want to expose the THP implementation details to users. Make <debugfs>/split_huge_pages accept a new command to do that.
By writing "<pid>,<vaddr_start>,<vaddr_end>" to <debugfs>/split_huge_pages, THPs within the given virtual address range from the process with the given pid are split. It is used to test split_huge_page function. In addition, a selftest program is added to tools/testing/selftests/vm to utilize the interface by splitting PMD THPs and PTE-mapped THPs.
This does not change the old behavior, i.e., writing 1 to the interface to split all THPs in the system.
Changelog:
From v5:
- Skipped special VMAs and other fixes. (suggested by Yang Shi)
Looks good to me. Reviewed-by: Yang Shi shy828301@gmail.com
Some nits below:
From v4:
- Fixed the error code return issue, spotted by kernel test robot lkp@intel.com.
From v3:
- Factored out split huge pages in the given pid code to a separate function.
- Added the missing put_page for not split pages.
- pr_debug -> pr_info, make reading results simpler.
From v2:
- Reused existing <debugfs>/split_huge_pages interface. (suggested by Yang Shi)
From v1:
- Removed unnecessary calling to vma_migratable, spotted by kernel test robot lkp@intel.com.
- Dropped the use of find_mm_struct and code it directly, since there is no need for the permission check in that function and the function is only available when migration is on.
- Added some comments in the selftest program to clarify how PTE-mapped THPs are formed.
Signed-off-by: Zi Yan ziy@nvidia.com
mm/huge_memory.c | 143 +++++++- tools/testing/selftests/vm/.gitignore | 1 + tools/testing/selftests/vm/Makefile | 1 + .../selftests/vm/split_huge_page_test.c | 318 ++++++++++++++++++ 4 files changed, 456 insertions(+), 7 deletions(-) create mode 100644 tools/testing/selftests/vm/split_huge_page_test.c
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index bff92dea5ab3..9bf9bc489228 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -7,6 +7,7 @@
#include <linux/mm.h> #include <linux/sched.h> +#include <linux/sched/mm.h> #include <linux/sched/coredump.h> #include <linux/sched/numa_balancing.h> #include <linux/highmem.h> @@ -2922,16 +2923,14 @@ static struct shrinker deferred_split_shrinker = { };
#ifdef CONFIG_DEBUG_FS -static int split_huge_pages_set(void *data, u64 val) +static void split_huge_pages_all(void) { struct zone *zone; struct page *page; unsigned long pfn, max_zone_pfn; unsigned long total = 0, split = 0;
if (val != 1)return -EINVAL;
pr_info("Split all THPs\n"); for_each_populated_zone(zone) { max_zone_pfn = zone_end_pfn(zone); for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {@@ -2959,11 +2958,141 @@ static int split_huge_pages_set(void *data, u64 val) }
pr_info("%lu of %lu THP split\n", split, total);+}
return 0;+static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
unsigned long vaddr_end)+{
int ret = 0;struct task_struct *task;struct mm_struct *mm;unsigned long total = 0, split = 0;unsigned long addr;vaddr_start &= PAGE_MASK;vaddr_end &= PAGE_MASK;/* Find the task_struct from pid */rcu_read_lock();task = find_task_by_vpid(pid);if (!task) {rcu_read_unlock();ret = -ESRCH;goto out;}get_task_struct(task);rcu_read_unlock();/* Find the mm_struct */mm = get_task_mm(task);put_task_struct(task);if (!mm) {ret = -EINVAL;goto out;}pr_info("Split huge pages in pid: %d, vaddr: [0x%lx - 0x%lx]\n",pid, vaddr_start, vaddr_end);mmap_read_lock(mm);/** always increase addr by PAGE_SIZE, since we could have a PTE page* table filled with PTE-mapped THPs, each of which is distinct.*/for (addr = vaddr_start; addr < vaddr_end; addr += PAGE_SIZE) {struct vm_area_struct *vma = find_vma(mm, addr);unsigned int follflags;struct page *page;if (!vma || addr < vma->vm_start)break;/* skip special VMA and hugetlb VMA */if (vma_is_special_huge(vma) || is_vm_hugetlb_page(vma)) {VM_IO vma should be skipped as well. And you may extract this into a helper?
Sure. Any name suggestion? :)
addr = vma->vm_end;continue;}/* FOLL_DUMP to ignore special (like zero) pages */follflags = FOLL_GET | FOLL_DUMP;page = follow_page(vma, addr, follflags);if (IS_ERR(page))continue;if (!page)continue;if (!is_transparent_hugepage(page))goto next;total++;if (!can_split_huge_page(compound_head(page), NULL))goto next;if (!trylock_page(page))goto next;if (!split_huge_page(page))split++;unlock_page(page);+next:
put_page(page);}mmap_read_unlock(mm);mmput(mm);pr_info("%lu of %lu THP split\n", split, total);+out:
return ret;} -DEFINE_DEBUGFS_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
"%llu\n");
+static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppops)+{
static DEFINE_MUTEX(split_debug_mutex);ssize_t ret;char input_buf[80]; /* hold pid, start_vaddr, end_vaddr */Why not move buf len macro in the following patch to this patch? Then you don't have to change the length again.
Sure.
Thanks for the comments.
-- Best Regards, Yan Zi