@@ -76,6 +76,8 @@
#define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */
+#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+
/* compatibility flags */
#define MAP_FILE 0
@@ -103,6 +103,8 @@
#define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */
+#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+
/* compatibility flags */
#define MAP_FILE 0
@@ -70,6 +70,8 @@
#define MADV_WIPEONFORK 71 /* Zero memory on fork, child only */
#define MADV_KEEPONFORK 72 /* Undo MADV_WIPEONFORK */
+#define MADV_COLLAPSE 73 /* Synchronous hugepage collapse */
+
#define MADV_HWPOISON 100 /* poison a page for testing */
#define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */
@@ -111,6 +111,8 @@
#define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */
+#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+
/* compatibility flags */
#define MAP_FILE 0
@@ -236,6 +236,9 @@ void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags,
int advice);
+int madvise_collapse(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end);
void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start,
unsigned long end, long adjust_next);
spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma);
@@ -392,6 +395,15 @@ static inline int hugepage_madvise(struct vm_area_struct *vma,
BUG();
return 0;
}
+
+static inline int madvise_collapse(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ BUG();
+ return 0;
+}
+
static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
unsigned long start,
unsigned long end,
@@ -77,6 +77,8 @@
#define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */
+#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+
/* compatibility flags */
#define MAP_FILE 0
@@ -846,6 +846,23 @@ static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
}
+static struct page *alloc_hpage(struct collapse_control *cc, gfp_t gfp,
+ int node)
+{
+ VM_BUG_ON_PAGE(cc->hpage, cc->hpage);
+
+ cc->hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
+ if (unlikely(!cc->hpage)) {
+ count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
+ cc->hpage = ERR_PTR(-ENOMEM);
+ return NULL;
+ }
+
+ prep_transhuge_page(cc->hpage);
+ count_vm_event(THP_COLLAPSE_ALLOC);
+ return cc->hpage;
+}
+
#ifdef CONFIG_NUMA
static int khugepaged_find_target_node(struct collapse_control *cc)
{
@@ -892,18 +909,7 @@ static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
static struct page *khugepaged_alloc_page(struct collapse_control *cc,
gfp_t gfp, int node)
{
- VM_BUG_ON_PAGE(cc->hpage, cc->hpage);
-
- cc->hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
- if (unlikely(!cc->hpage)) {
- count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
- cc->hpage = ERR_PTR(-ENOMEM);
- return NULL;
- }
-
- prep_transhuge_page(cc->hpage);
- count_vm_event(THP_COLLAPSE_ALLOC);
- return cc->hpage;
+ return alloc_hpage(cc, gfp, node);
}
#else
static int khugepaged_find_target_node(struct collapse_control *cc)
@@ -2469,3 +2475,122 @@ void khugepaged_min_free_kbytes_update(void)
set_recommended_min_free_kbytes();
mutex_unlock(&khugepaged_mutex);
}
+
+static void madvise_collapse_cleanup_page(struct page **hpage)
+{
+ if (!IS_ERR(*hpage) && *hpage)
+ put_page(*hpage);
+ *hpage = NULL;
+}
+
+static int madvise_collapse_errno(enum scan_result r)
+{
+ switch (r) {
+ case SCAN_PMD_NULL:
+ case SCAN_ADDRESS_RANGE:
+ case SCAN_VMA_NULL:
+ case SCAN_PTE_NON_PRESENT:
+ case SCAN_PAGE_NULL:
+ /*
+ * Addresses in the specified range are not currently mapped,
+ * or are outside the AS of the process.
+ */
+ return -ENOMEM;
+ case SCAN_ALLOC_HUGE_PAGE_FAIL:
+ case SCAN_CGROUP_CHARGE_FAIL:
+ /* A kernel resource was temporarily unavailable. */
+ return -EAGAIN;
+ default:
+ return -EINVAL;
+ }
+}
+
+int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ struct collapse_control cc = {
+ .last_target_node = NUMA_NO_NODE,
+ .hpage = NULL,
+ .alloc_hpage = &alloc_hpage,
+ };
+ struct mm_struct *mm = vma->vm_mm;
+ struct collapse_result cr;
+ unsigned long hstart, hend, addr;
+ int thps = 0, nr_hpages = 0;
+
+ BUG_ON(vma->vm_start > start);
+ BUG_ON(vma->vm_end < end);
+
+ *prev = vma;
+
+ if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file)
+ return -EINVAL;
+
+ hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
+ hend = end & HPAGE_PMD_MASK;
+ nr_hpages = (hend - hstart) >> HPAGE_PMD_SHIFT;
+
+ if (hstart >= hend || !transparent_hugepage_active(vma))
+ return -EINVAL;
+
+ mmgrab(mm);
+ lru_add_drain();
+
+ for (addr = hstart; ; ) {
+ mmap_assert_locked(mm);
+ cond_resched();
+ memset(&cr, 0, sizeof(cr));
+
+ if (unlikely(khugepaged_test_exit(mm)))
+ break;
+
+ memset(cc.node_load, 0, sizeof(cc.node_load));
+ khugepaged_scan_pmd(mm, vma, addr, &cc, &cr);
+ if (cr.dropped_mmap_lock)
+ *prev = NULL; /* tell madvise we dropped mmap_lock */
+
+ switch (cr.result) {
+ /* Whitelisted set of results where continuing OK */
+ case SCAN_SUCCEED:
+ case SCAN_PMD_MAPPED:
+ ++thps;
+ case SCAN_PMD_NULL:
+ case SCAN_PTE_NON_PRESENT:
+ case SCAN_PTE_UFFD_WP:
+ case SCAN_PAGE_RO:
+ case SCAN_LACK_REFERENCED_PAGE:
+ case SCAN_PAGE_NULL:
+ case SCAN_PAGE_COUNT:
+ case SCAN_PAGE_LOCK:
+ case SCAN_PAGE_COMPOUND:
+ break;
+ case SCAN_PAGE_LRU:
+ lru_add_drain_all();
+ goto retry;
+ default:
+ /* Other error, exit */
+ goto break_loop;
+ }
+ addr += HPAGE_PMD_SIZE;
+ if (addr >= hend)
+ break;
+retry:
+ if (cr.dropped_mmap_lock) {
+ mmap_read_lock(mm);
+ if (hugepage_vma_revalidate(mm, addr, &vma))
+ goto out;
+ }
+ madvise_collapse_cleanup_page(&cc.hpage);
+ }
+
+break_loop:
+ /* madvise_walk_vmas() expects us to hold mmap_lock on return */
+ if (cr.dropped_mmap_lock)
+ mmap_read_lock(mm);
+out:
+ mmap_assert_locked(mm);
+ madvise_collapse_cleanup_page(&cc.hpage);
+ mmdrop(mm);
+
+ return thps == nr_hpages ? 0 : madvise_collapse_errno(cr.result);
+}
@@ -59,6 +59,7 @@ static int madvise_need_mmap_write(int behavior)
case MADV_FREE:
case MADV_POPULATE_READ:
case MADV_POPULATE_WRITE:
+ case MADV_COLLAPSE:
return 0;
default:
/* be safe, default to 1. list exceptions explicitly */
@@ -1051,6 +1052,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
if (error)
goto out;
break;
+ case MADV_COLLAPSE:
+ return madvise_collapse(vma, prev, start, end);
}
anon_name = anon_vma_name(vma);
@@ -1144,6 +1147,7 @@ madvise_behavior_valid(int behavior)
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
case MADV_HUGEPAGE:
case MADV_NOHUGEPAGE:
+ case MADV_COLLAPSE:
#endif
case MADV_DONTDUMP:
case MADV_DODUMP:
@@ -1333,6 +1337,7 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
* MADV_NOHUGEPAGE - mark the given range as not worth being backed by
* transparent huge pages so the existing pages will not be
* coalesced into THP and new pages will not be allocated as THP.
+ * MADV_COLLAPSE - synchronously coalesce pages into new THP.
* MADV_DONTDUMP - the application wants to prevent pages in the given range
* from being included in its core dump.
* MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
This idea was introduced by David Rientjes[1], and the semantics and implementation were introduced and discussed in a previous PATCH RFC[2]. Introduce a new madvise mode, MADV_COLLAPSE, that allows users to request a synchronous collapse of memory at their own expense. The benefits of this approach are: * CPU is charged to the process that wants to spend the cycles for the THP * avoid unpredictable timing of khugepaged collapse Immediate users of this new functionality include: * immediately back executable text by hugepages. Current support provided by CONFIG_READ_ONLY_THP_FOR_FS may take too long on a large system. * malloc implementations that manage memory in hugepage-sized chunks, but sometimes subrelease memory back to the system in native-sized chunks via MADV_DONTNEED; zapping the pmd. Later, when the memory is hot, the implementation could madvise(MADV_COLLAPSE) to re-back the memory by THP to regain TLB performance. Allocation semantics are the same as khugepaged, and depend on (1) the active sysfs settings /sys/kernel/mm/transparent_hugepage/enabled and /sys/kernel/mm/transparent_hugepage/khugepaged/defrag, and (2) the VMA flags of the memory range being collapsed. Only privately-mapped anon memory is supported for now. [1] https://lore.kernel.org/linux-mm/d098c392-273a-36a4-1a29-59731cdf5d3d@google.com/ [2] https://lore.kernel.org/linux-mm/20220308213417.1407042-1-zokeefe@google.com/ Suggested-by: David Rientjes <rientjes@google.com> Signed-off-by: Zach O'Keefe <zokeefe@google.com> Reported-by: kernel test robot <lkp@intel.com> --- arch/alpha/include/uapi/asm/mman.h | 2 + arch/mips/include/uapi/asm/mman.h | 2 + arch/parisc/include/uapi/asm/mman.h | 2 + arch/xtensa/include/uapi/asm/mman.h | 2 + include/linux/huge_mm.h | 12 ++ include/uapi/asm-generic/mman-common.h | 2 + mm/khugepaged.c | 149 +++++++++++++++++++++++-- mm/madvise.c | 5 + 8 files changed, 164 insertions(+), 12 deletions(-)