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Subject[RFC PATCH 22/26] madvise: add uapi for HugeTLB HGM collapse: MADV_COLLAPSE
From
This commit is co-opting the same madvise mode that is being introduced
by zokeefe@google.com to manually collapse THPs[1].

As with the rest of the high-granularity mapping support, MADV_COLLAPSE
is only supported for shared VMAs right now.

[1] https://lore.kernel.org/linux-mm/20220604004004.954674-10-zokeefe@google.com/

Signed-off-by: James Houghton <jthoughton@google.com>
---
include/uapi/asm-generic/mman-common.h | 2 ++
mm/madvise.c | 23 +++++++++++++++++++++++
2 files changed, 25 insertions(+)

diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 6c1aa92a92e4..b686920ca731 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -77,6 +77,8 @@

#define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */

+#define MADV_COLLAPSE 25 /* collapse an address range into hugepages */
+
/* compatibility flags */
#define MAP_FILE 0

diff --git a/mm/madvise.c b/mm/madvise.c
index d7b4f2602949..c624c0f02276 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -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 */
@@ -981,6 +982,20 @@ static long madvise_remove(struct vm_area_struct *vma,
return error;
}

+static int madvise_collapse(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ bool shared = vma->vm_flags & VM_SHARED;
+ *prev = vma;
+
+ /* Only allow collapsing for HGM-enabled, shared mappings. */
+ if (!is_vm_hugetlb_page(vma) || !hugetlb_hgm_enabled(vma) || !shared)
+ return -EINVAL;
+
+ return hugetlb_collapse(vma->vm_mm, vma, start, end);
+}
+
/*
* Apply an madvise behavior to a region of a vma. madvise_update_vma
* will handle splitting a vm area into separate areas, each area with its own
@@ -1011,6 +1026,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
case MADV_POPULATE_READ:
case MADV_POPULATE_WRITE:
return madvise_populate(vma, prev, start, end, behavior);
+ case MADV_COLLAPSE:
+ return madvise_collapse(vma, prev, start, end);
case MADV_NORMAL:
new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
break;
@@ -1158,6 +1175,9 @@ madvise_behavior_valid(int behavior)
#ifdef CONFIG_MEMORY_FAILURE
case MADV_SOFT_OFFLINE:
case MADV_HWPOISON:
+#endif
+#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
+ case MADV_COLLAPSE:
#endif
return true;

@@ -1351,6 +1371,9 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
* triggering read faults if required
* MADV_POPULATE_WRITE - populate (prefault) page tables writable by
* triggering write faults if required
+ * MADV_COLLAPSE - collapse a high-granularity HugeTLB mapping into huge
+ * mappings. This is useful after an entire hugepage has been
+ * mapped with individual small UFFDIO_CONTINUE operations.
*
* return values:
* zero - success
--
2.37.0.rc0.161.g10f37bed90-goog
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