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Message-Id: <20220825101037.96517-8-zhengqi.arch@bytedance.com>
Date: Thu, 25 Aug 2022 18:10:37 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: akpm@...ux-foundation.org, david@...hat.com,
kirill.shutemov@...ux.intel.com, mika.penttila@...tfour.com,
jgg@...dia.com, tglx@...utronix.de, willy@...radead.org
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
muchun.song@...ux.dev, Qi Zheng <zhengqi.arch@...edance.com>
Subject: [RFC PATCH 7/7] mm: add proc interface to free user PTE page table pages
Add /proc/sys/vm/free_ptes file to procfs, when pid is written
to the file, we will traverse its process address space, find
and free empty PTE pages or zero PTE pages.
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
include/linux/pte_ref.h | 5 ++
kernel/sysctl.c | 12 ++++
mm/pte_ref.c | 126 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 143 insertions(+)
diff --git a/include/linux/pte_ref.h b/include/linux/pte_ref.h
index ab49c7fac120..f7e244129291 100644
--- a/include/linux/pte_ref.h
+++ b/include/linux/pte_ref.h
@@ -16,6 +16,11 @@ void track_pte_set(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
pte_t pte);
void track_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
pte_t pte);
+
+int free_ptes_sysctl_handler(struct ctl_table *table, int write,
+ void *buffer, size_t *length, loff_t *ppos);
+extern int sysctl_free_ptes_pid;
+
#else /* !CONFIG_FREE_USER_PTE */
static inline void pte_ref_init(pgtable_t pte)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 35d034219513..14e1a9841cb8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -64,6 +64,7 @@
#include <linux/mount.h>
#include <linux/userfaultfd_k.h>
#include <linux/pid.h>
+#include <linux/pte_ref.h>
#include "../lib/kstrtox.h"
@@ -2153,6 +2154,17 @@ static struct ctl_table vm_table[] = {
.extra1 = SYSCTL_ONE,
.extra2 = SYSCTL_FOUR,
},
+#ifdef CONFIG_FREE_USER_PTE
+ {
+ .procname = "free_ptes",
+ .data = &sysctl_free_ptes_pid,
+ .maxlen = sizeof(int),
+ .mode = 0200,
+ .proc_handler = free_ptes_sysctl_handler,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_INT_MAX,
+ },
+#endif
#ifdef CONFIG_COMPACTION
{
.procname = "compact_memory",
diff --git a/mm/pte_ref.c b/mm/pte_ref.c
index 818821d068af..e7080a3100a6 100644
--- a/mm/pte_ref.c
+++ b/mm/pte_ref.c
@@ -6,6 +6,14 @@
*/
#include <linux/pgtable.h>
#include <linux/pte_ref.h>
+#include <linux/mm.h>
+#include <linux/pagewalk.h>
+#include <linux/sched/mm.h>
+#include <linux/jump_label.h>
+#include <linux/hugetlb.h>
+#include <asm/tlbflush.h>
+
+#include "internal.h"
#ifdef CONFIG_FREE_USER_PTE
@@ -105,4 +113,122 @@ void track_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
}
EXPORT_SYMBOL(track_pte_clear);
+#ifdef CONFIG_DEBUG_VM
+void pte_free_debug(pmd_t pmd)
+{
+ pte_t *ptep = (pte_t *)pmd_page_vaddr(pmd);
+ int i = 0;
+
+ for (i = 0; i < PTRS_PER_PTE; i++, ptep++) {
+ pte_t pte = *ptep;
+ BUG_ON(!(pte_none(pte) || is_zero_pfn(pte_pfn(pte))));
+ }
+}
+#else
+static inline void pte_free_debug(pmd_t pmd)
+{
+}
+#endif
+
+
+static int kfreeptd_pmd_entry(pmd_t *pmd, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pmd_t pmdval;
+ pgtable_t page;
+ struct mm_struct *mm = walk->mm;
+ struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0);
+ spinlock_t *ptl;
+ bool free = false;
+ unsigned long haddr = addr & PMD_MASK;
+
+ if (pmd_trans_unstable(pmd))
+ goto out;
+
+ mmap_read_unlock(mm);
+ mmap_write_lock(mm);
+
+ if (mm_find_pmd(mm, addr) != pmd)
+ goto unlock_out;
+
+ ptl = pmd_lock(mm, pmd);
+ pmdval = *pmd;
+ if (pmd_none(pmdval) || pmd_leaf(pmdval)) {
+ spin_unlock(ptl);
+ goto unlock_out;
+ }
+ page = pmd_pgtable(pmdval);
+ if (!pte_mapped_count(page) || pte_zero_count(page) == PTRS_PER_PTE) {
+ pmd_clear(pmd);
+ flush_tlb_range(&vma, haddr, haddr + PMD_SIZE);
+ free = true;
+ }
+ spin_unlock(ptl);
+
+unlock_out:
+ mmap_write_unlock(mm);
+ mmap_read_lock(mm);
+
+ if (free) {
+ pte_free_debug(pmdval);
+ mm_dec_nr_ptes(mm);
+ pgtable_pte_page_dtor(page);
+ __free_page(page);
+ }
+
+out:
+ cond_resched();
+ return 0;
+}
+
+static const struct mm_walk_ops kfreeptd_walk_ops = {
+ .pmd_entry = kfreeptd_pmd_entry,
+};
+
+int sysctl_free_ptes_pid;
+int free_ptes_sysctl_handler(struct ctl_table *table, int write,
+ void *buffer, size_t *length, loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
+ if (ret)
+ return ret;
+ if (write) {
+ struct task_struct *task;
+ struct mm_struct *mm;
+
+ rcu_read_lock();
+ task = find_task_by_vpid(sysctl_free_ptes_pid);
+ if (!task) {
+ rcu_read_unlock();
+ return -ESRCH;
+ }
+ mm = get_task_mm(task);
+ rcu_read_unlock();
+
+ if (!mm) {
+ mmput(mm);
+ return -ESRCH;
+ }
+
+ do {
+ ret = -EBUSY;
+
+ if (mmap_read_trylock(mm)) {
+ ret = walk_page_range(mm, FIRST_USER_ADDRESS,
+ ULONG_MAX,
+ &kfreeptd_walk_ops, NULL);
+
+ mmap_read_unlock(mm);
+ }
+
+ cond_resched();
+ } while (ret == -EAGAIN);
+
+ mmput(mm);
+ }
+ return ret;
+}
+
#endif /* CONFIG_FREE_USER_PTE */
--
2.20.1
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