mm/khugepaged: delete khugepaged_collapse_pte_mapped_thps()

Now that retract_page_tables() can retract page tables reliably, without
depending on trylocks, delete all the apparatus for khugepaged to try
again later: khugepaged_collapse_pte_mapped_thps() etc; and free up the
per-mm memory which was set aside for that in the khugepaged_mm_slot.

But one part of that is worth keeping: when hpage_collapse_scan_file()
found SCAN_PTE_MAPPED_HUGEPAGE, that address was noted in the mm_slot to
be tried for retraction later - catching, for example, page tables where a
reversible mprotect() of a portion had required splitting the pmd, but now
it can be recollapsed.  Call collapse_pte_mapped_thp() directly in this
case (why was it deferred before?  I assume an issue with needing
mmap_lock for write, but now it's only needed for read).

[hughd@google.com: fix mmap_locked handlng]
Link: https://lkml.kernel.org/r/bfc6cab2-497f-32bf-dd5-98dc1987e4a9@google.com
Link: https://lkml.kernel.org/r/a5dce57-6dfa-5559-4698-e817eb2f993@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 53d1788..9a6e0d5 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -93,8 +93,6 @@ static DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
 
 static struct kmem_cache *mm_slot_cache __read_mostly;
 
-#define MAX_PTE_MAPPED_THP 8
-
 struct collapse_control {
        bool is_khugepaged;
 
@@ -108,15 +106,9 @@ struct collapse_control {
 /**
  * struct khugepaged_mm_slot - khugepaged information per mm that is being scanned
  * @slot: hash lookup from mm to mm_slot
- * @nr_pte_mapped_thp: number of pte mapped THP
- * @pte_mapped_thp: address array corresponding pte mapped THP
  */
 struct khugepaged_mm_slot {
        struct mm_slot slot;
-
-       /* pte-mapped THP in this mm */
-       int nr_pte_mapped_thp;
-       unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
 };
 
 /**
@@ -1441,50 +1433,6 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
 }
 
 #ifdef CONFIG_SHMEM
-/*
- * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
- * khugepaged should try to collapse the page table.
- *
- * Note that following race exists:
- * (1) khugepaged calls khugepaged_collapse_pte_mapped_thps() for mm_struct A,
- *     emptying the A's ->pte_mapped_thp[] array.
- * (2) MADV_COLLAPSE collapses some file extent with target mm_struct B, and
- *     retract_page_tables() finds a VMA in mm_struct A mapping the same extent
- *     (at virtual address X) and adds an entry (for X) into mm_struct A's
- *     ->pte-mapped_thp[] array.
- * (3) khugepaged calls khugepaged_collapse_scan_file() for mm_struct A at X,
- *     sees a pte-mapped THP (SCAN_PTE_MAPPED_HUGEPAGE) and adds an entry
- *     (for X) into mm_struct A's ->pte-mapped_thp[] array.
- * Thus, it's possible the same address is added multiple times for the same
- * mm_struct.  Should this happen, we'll simply attempt
- * collapse_pte_mapped_thp() multiple times for the same address, under the same
- * exclusive mmap_lock, and assuming the first call is successful, subsequent
- * attempts will return quickly (without grabbing any additional locks) when
- * a huge pmd is found in find_pmd_or_thp_or_none().  Since this is a cheap
- * check, and since this is a rare occurrence, the cost of preventing this
- * "multiple-add" is thought to be more expensive than just handling it, should
- * it occur.
- */
-static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
-                                         unsigned long addr)
-{
-       struct khugepaged_mm_slot *mm_slot;
-       struct mm_slot *slot;
-       bool ret = false;
-
-       VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
-
-       spin_lock(&khugepaged_mm_lock);
-       slot = mm_slot_lookup(mm_slots_hash, mm);
-       mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
-       if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP)) {
-               mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
-               ret = true;
-       }
-       spin_unlock(&khugepaged_mm_lock);
-       return ret;
-}
-
 /* hpage must be locked, and mmap_lock must be held */
 static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
                        pmd_t *pmdp, struct page *hpage)
@@ -1708,29 +1656,6 @@ drop_hpage:
        return result;
 }
 
-static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot)
-{
-       struct mm_slot *slot = &mm_slot->slot;
-       struct mm_struct *mm = slot->mm;
-       int i;
-
-       if (likely(mm_slot->nr_pte_mapped_thp == 0))
-               return;
-
-       if (!mmap_write_trylock(mm))
-               return;
-
-       if (unlikely(hpage_collapse_test_exit(mm)))
-               goto out;
-
-       for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
-               collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i], false);
-
-out:
-       mm_slot->nr_pte_mapped_thp = 0;
-       mmap_write_unlock(mm);
-}
-
 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 {
        struct vm_area_struct *vma;
@@ -2371,16 +2296,6 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
 {
        BUILD_BUG();
 }
-
-static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot)
-{
-}
-
-static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
-                                         unsigned long addr)
-{
-       return false;
-}
 #endif
 
 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
@@ -2410,7 +2325,6 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
                khugepaged_scan.mm_slot = mm_slot;
        }
        spin_unlock(&khugepaged_mm_lock);
-       khugepaged_collapse_pte_mapped_thps(mm_slot);
 
        mm = slot->mm;
        /*
@@ -2463,36 +2377,27 @@ skip:
                                                khugepaged_scan.address);
 
                                mmap_read_unlock(mm);
-                               *result = hpage_collapse_scan_file(mm,
-                                                                  khugepaged_scan.address,
-                                                                  file, pgoff, cc);
                                mmap_locked = false;
+                               *result = hpage_collapse_scan_file(mm,
+                                       khugepaged_scan.address, file, pgoff, cc);
                                fput(file);
+                               if (*result == SCAN_PTE_MAPPED_HUGEPAGE) {
+                                       mmap_read_lock(mm);
+                                       if (hpage_collapse_test_exit(mm))
+                                               goto breakouterloop;
+                                       *result = collapse_pte_mapped_thp(mm,
+                                               khugepaged_scan.address, false);
+                                       if (*result == SCAN_PMD_MAPPED)
+                                               *result = SCAN_SUCCEED;
+                                       mmap_read_unlock(mm);
+                               }
                        } else {
                                *result = hpage_collapse_scan_pmd(mm, vma,
-                                                                 khugepaged_scan.address,
-                                                                 &mmap_locked,
-                                                                 cc);
+                                       khugepaged_scan.address, &mmap_locked, cc);
                        }
-                       switch (*result) {
-                       case SCAN_PTE_MAPPED_HUGEPAGE: {
-                               pmd_t *pmd;
-
-                               *result = find_pmd_or_thp_or_none(mm,
-                                                                 khugepaged_scan.address,
-                                                                 &pmd);
-                               if (*result != SCAN_SUCCEED)
-                                       break;
-                               if (!khugepaged_add_pte_mapped_thp(mm,
-                                                                  khugepaged_scan.address))
-                                       break;
-                       } fallthrough;
-                       case SCAN_SUCCEED:
+
+                       if (*result == SCAN_SUCCEED)
                                ++khugepaged_pages_collapsed;
-                               break;
-                       default:
-                               break;
-                       }
 
                        /* move to next address */
                        khugepaged_scan.address += HPAGE_PMD_SIZE;