[PATCH 3.16 058/131] rmap: drop support of non-linear mappings

From: Ben Hutchings
Date: Sat Sep 29 2018 - 17:49:43 EST

3.16.59-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

commit 27ba0644ea9dfe6e7693abc85837b60e40583b96 upstream.

We don't create non-linear mappings anymore. Let's drop code which
handles them in rmap.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
- Deleted code is slightly different
- Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/Documentation/cachetlb.txt
+++ b/Documentation/cachetlb.txt
@@ -317,10 +317,10 @@ maps this page at its virtual address.
about doing this.

The idea is, first at flush_dcache_page() time, if
- page->mapping->i_mmap is an empty tree and ->i_mmap_nonlinear
- an empty list, just mark the architecture private page flag bit.
- Later, in update_mmu_cache(), a check is made of this flag bit,
- and if set the flush is done and the flag bit is cleared.
+ page->mapping->i_mmap is an empty tree, just mark the architecture
+ private page flag bit. Later, in update_mmu_cache(), a check is
+ made of this flag bit, and if set the flush is done and the flag
+ bit is cleared.

IMPORTANT NOTE: It is often important, if you defer the flush,
that the actual flush occurs on the same CPU
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -352,7 +352,6 @@ void address_space_init_once(struct addr
INIT_LIST_HEAD(&mapping->private_list);
spin_lock_init(&mapping->private_lock);
mapping->i_mmap = RB_ROOT;
- INIT_LIST_HEAD(&mapping->i_mmap_nonlinear);
}
EXPORT_SYMBOL(address_space_init_once);

--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -395,7 +395,6 @@ struct address_space {
spinlock_t tree_lock; /* and lock protecting it */
unsigned int i_mmap_writable;/* count VM_SHARED mappings */
struct rb_root i_mmap; /* tree of private and shared mappings */
- struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
struct mutex i_mmap_mutex; /* protect tree, count, list */
/* Protected by tree_lock together with the radix tree */
unsigned long nrpages; /* number of total pages */
@@ -467,8 +466,7 @@ int mapping_tagged(struct address_space
*/
static inline int mapping_mapped(struct address_space *mapping)
{
- return !RB_EMPTY_ROOT(&mapping->i_mmap) ||
- !list_empty(&mapping->i_mmap_nonlinear);
+ return !RB_EMPTY_ROOT(&mapping->i_mmap);
}

/*
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1728,12 +1728,6 @@ struct vm_area_struct *vma_interval_tree
for (vma = vma_interval_tree_iter_first(root, start, last); \
vma; vma = vma_interval_tree_iter_next(vma, start, last))

-static inline void vma_nonlinear_insert(struct vm_area_struct *vma,
- struct list_head *list)
-{
- list_add_tail(&vma->shared.nonlinear, list);
-}
-
void anon_vma_interval_tree_insert(struct anon_vma_chain *node,
struct rb_root *root);
void anon_vma_interval_tree_remove(struct anon_vma_chain *node,
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -272,15 +272,13 @@ struct vm_area_struct {

/*
* For areas with an address space and backing store,
- * linkage into the address_space->i_mmap interval tree, or
- * linkage of vma in the address_space->i_mmap_nonlinear list.
+ * linkage into the address_space->i_mmap interval tree.
*/
union {
struct {
struct rb_node rb;
unsigned long rb_subtree_last;
} linear;
- struct list_head nonlinear;
} shared;

/*
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -232,7 +232,6 @@ int page_mapped_in_vma(struct page *page
* arg: passed to rmap_one() and invalid_vma()
* rmap_one: executed on each vma where page is mapped
* done: for checking traversing termination condition
- * file_nonlinear: for handling file nonlinear mapping
* anon_lock: for getting anon_lock by optimized way rather than default
* invalid_vma: for skipping uninterested vma
*/
@@ -241,7 +240,6 @@ struct rmap_walk_control {
int (*rmap_one)(struct page *page, struct vm_area_struct *vma,
unsigned long addr, void *arg);
int (*done)(struct page *page);
- int (*file_nonlinear)(struct page *, struct address_space *, void *arg);
struct anon_vma *(*anon_lock)(struct page *page);
bool (*invalid_vma)(struct vm_area_struct *vma, void *arg);
};
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -430,12 +430,8 @@ static int dup_mmap(struct mm_struct *mm
mapping->i_mmap_writable++;
flush_dcache_mmap_lock(mapping);
/* insert tmp into the share list, just after mpnt */
- if (unlikely(tmp->vm_flags & VM_NONLINEAR))
- vma_nonlinear_insert(tmp,
- &mapping->i_mmap_nonlinear);
- else
- vma_interval_tree_insert_after(tmp, mpnt,
- &mapping->i_mmap);
+ vma_interval_tree_insert_after(tmp, mpnt,
+ &mapping->i_mmap);
flush_dcache_mmap_unlock(mapping);
mutex_unlock(&mapping->i_mmap_mutex);
}
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -181,37 +181,6 @@ out:
}

/*
- * Congratulations to trinity for discovering this bug.
- * mm/fremap.c's remap_file_pages() accepts any range within a single vma to
- * convert that vma to VM_NONLINEAR; and generic_file_remap_pages() will then
- * replace the specified range by file ptes throughout (maybe populated after).
- * If page migration finds a page within that range, while it's still located
- * by vma_interval_tree rather than lost to i_mmap_nonlinear list, no problem:
- * zap_pte() clears the temporary migration entry before mmap_sem is dropped.
- * But if the migrating page is in a part of the vma outside the range to be
- * remapped, then it will not be cleared, and remove_migration_ptes() needs to
- * deal with it. Fortunately, this part of the vma is of course still linear,
- * so we just need to use linear location on the nonlinear list.
- */
-static int remove_linear_migration_ptes_from_nonlinear(struct page *page,
- struct address_space *mapping, void *arg)
-{
- struct vm_area_struct *vma;
- /* hugetlbfs does not support remap_pages, so no huge pgoff worries */
- pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
- unsigned long addr;
-
- list_for_each_entry(vma,
- &mapping->i_mmap_nonlinear, shared.nonlinear) {
-
- addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
- if (addr >= vma->vm_start && addr < vma->vm_end)
- remove_migration_pte(page, vma, addr, arg);
- }
- return SWAP_AGAIN;
-}
-
-/*
* Get rid of all migration entries and replace them by
* references to the indicated page.
*/
@@ -220,7 +189,6 @@ static void remove_migration_ptes(struct
struct rmap_walk_control rwc = {
.rmap_one = remove_migration_pte,
.arg = old,
- .file_nonlinear = remove_linear_migration_ptes_from_nonlinear,
};

rmap_walk(new, &rwc);
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -219,10 +219,7 @@ static void __remove_shared_vm_struct(st
mapping->i_mmap_writable--;

flush_dcache_mmap_lock(mapping);
- if (unlikely(vma->vm_flags & VM_NONLINEAR))
- list_del_init(&vma->shared.nonlinear);
- else
- vma_interval_tree_remove(vma, &mapping->i_mmap);
+ vma_interval_tree_remove(vma, &mapping->i_mmap);
flush_dcache_mmap_unlock(mapping);
}

@@ -639,10 +636,7 @@ static void __vma_link_file(struct vm_ar
mapping->i_mmap_writable++;

flush_dcache_mmap_lock(mapping);
- if (unlikely(vma->vm_flags & VM_NONLINEAR))
- vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
- else
- vma_interval_tree_insert(vma, &mapping->i_mmap);
+ vma_interval_tree_insert(vma, &mapping->i_mmap);
flush_dcache_mmap_unlock(mapping);
}
}
@@ -777,14 +771,11 @@ again: remove_next = 1 + (end > next->

if (file) {
mapping = file->f_mapping;
- if (!(vma->vm_flags & VM_NONLINEAR)) {
- root = &mapping->i_mmap;
- uprobe_munmap(vma, vma->vm_start, vma->vm_end);
-
- if (adjust_next)
- uprobe_munmap(next, next->vm_start,
- next->vm_end);
- }
+ root = &mapping->i_mmap;
+ uprobe_munmap(vma, vma->vm_start, vma->vm_end);
+
+ if (adjust_next)
+ uprobe_munmap(next, next->vm_start, next->vm_end);

mutex_lock(&mapping->i_mmap_mutex);
if (insert) {
@@ -3187,8 +3178,7 @@ static void vm_lock_mapping(struct mm_st
*
* mmap_sem in write mode is required in order to block all operations
* that could modify pagetables and free pages without need of
- * altering the vma layout (for example populate_range() with
- * nonlinear vmas). It's also needed in write mode to avoid new
+ * altering the vma layout. It's also needed in write mode to avoid new
* anon_vmas to be associated with existing vmas.
*
* A single task can't take more than one mm_take_all_locks() in a row
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -597,9 +597,8 @@ unsigned long page_address_in_vma(struct
if (!vma->anon_vma || !page__anon_vma ||
vma->anon_vma->root != page__anon_vma->root)
return -EFAULT;
- } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
- if (!vma->vm_file ||
- vma->vm_file->f_mapping != page->mapping)
+ } else if (page->mapping) {
+ if (!vma->vm_file || vma->vm_file->f_mapping != page->mapping)
return -EFAULT;
} else
return -EFAULT;
@@ -1286,7 +1285,6 @@ static int try_to_unmap_one(struct page
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
set_pte_at(mm, address, pte, swp_pte);
- BUG_ON(pte_file(*pte));
} else if (IS_ENABLED(CONFIG_MIGRATION) &&
(flags & TTU_MIGRATION)) {
/* Establish migration entry for a file page */
@@ -1328,207 +1326,6 @@ out_mlock:
return ret;
}

-/*
- * objrmap doesn't work for nonlinear VMAs because the assumption that
- * offset-into-file correlates with offset-into-virtual-addresses does not hold.
- * Consequently, given a particular page and its ->index, we cannot locate the
- * ptes which are mapping that page without an exhaustive linear search.
- *
- * So what this code does is a mini "virtual scan" of each nonlinear VMA which
- * maps the file to which the target page belongs. The ->vm_private_data field
- * holds the current cursor into that scan. Successive searches will circulate
- * around the vma's virtual address space.
- *
- * So as more replacement pressure is applied to the pages in a nonlinear VMA,
- * more scanning pressure is placed against them as well. Eventually pages
- * will become fully unmapped and are eligible for eviction.
- *
- * For very sparsely populated VMAs this is a little inefficient - chances are
- * there there won't be many ptes located within the scan cluster. In this case
- * maybe we could scan further - to the end of the pte page, perhaps.
- *
- * Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can
- * acquire it without blocking. If vma locked, mlock the pages in the cluster,
- * rather than unmapping them. If we encounter the "check_page" that vmscan is
- * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
- */
-#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE)
-#define CLUSTER_MASK (~(CLUSTER_SIZE - 1))
-
-static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
- struct vm_area_struct *vma, struct page *check_page)
-{
- struct mm_struct *mm = vma->vm_mm;
- pmd_t *pmd;
- pte_t *pte;
- pte_t pteval;
- spinlock_t *ptl;
- struct page *page;
- unsigned long address;
- unsigned long mmun_start; /* For mmu_notifiers */
- unsigned long mmun_end; /* For mmu_notifiers */
- unsigned long end;
- int ret = SWAP_AGAIN;
- int locked_vma = 0;
-
- address = (vma->vm_start + cursor) & CLUSTER_MASK;
- end = address + CLUSTER_SIZE;
- if (address < vma->vm_start)
- address = vma->vm_start;
- if (end > vma->vm_end)
- end = vma->vm_end;
-
- pmd = mm_find_pmd(mm, address);
- if (!pmd)
- return ret;
-
- mmun_start = address;
- mmun_end = end;
- mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
-
- /*
- * If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
- * keep the sem while scanning the cluster for mlocking pages.
- */
- if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
- locked_vma = (vma->vm_flags & VM_LOCKED);
- if (!locked_vma)
- up_read(&vma->vm_mm->mmap_sem); /* don't need it */
- }
-
- pte = pte_offset_map_lock(mm, pmd, address, &ptl);
-
- /* Update high watermark before we lower rss */
- update_hiwater_rss(mm);
-
- for (; address < end; pte++, address += PAGE_SIZE) {
- if (!pte_present(*pte))
- continue;
- page = vm_normal_page(vma, address, *pte);
- BUG_ON(!page || PageAnon(page));
-
- if (locked_vma) {
- if (page == check_page) {
- /* we know we have check_page locked */
- mlock_vma_page(page);
- ret = SWAP_MLOCK;
- } else if (trylock_page(page)) {
- /*
- * If we can lock the page, perform mlock.
- * Otherwise leave the page alone, it will be
- * eventually encountered again later.
- */
- mlock_vma_page(page);
- unlock_page(page);
- }
- continue; /* don't unmap */
- }
-
- if (ptep_clear_flush_young_notify(vma, address, pte))
- continue;
-
- /* Nuke the page table entry. */
- flush_cache_page(vma, address, pte_pfn(*pte));
- pteval = ptep_clear_flush(vma, address, pte);
-
- /* If nonlinear, store the file page offset in the pte. */
- if (page->index != linear_page_index(vma, address)) {
- pte_t ptfile = pgoff_to_pte(page->index);
- if (pte_soft_dirty(pteval))
- ptfile = pte_file_mksoft_dirty(ptfile);
- set_pte_at(mm, address, pte, ptfile);
- }
-
- /* Move the dirty bit to the physical page now the pte is gone. */
- if (pte_dirty(pteval))
- set_page_dirty(page);
-
- page_remove_rmap(page);
- page_cache_release(page);
- dec_mm_counter(mm, MM_FILEPAGES);
- (*mapcount)--;
- }
- pte_unmap_unlock(pte - 1, ptl);
- mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
- if (locked_vma)
- up_read(&vma->vm_mm->mmap_sem);
- return ret;
-}
-
-static int try_to_unmap_nonlinear(struct page *page,
- struct address_space *mapping, void *arg)
-{
- struct vm_area_struct *vma;
- int ret = SWAP_AGAIN;
- unsigned long cursor;
- unsigned long max_nl_cursor = 0;
- unsigned long max_nl_size = 0;
- unsigned int mapcount;
-
- list_for_each_entry(vma,
- &mapping->i_mmap_nonlinear, shared.nonlinear) {
-
- cursor = (unsigned long) vma->vm_private_data;
- if (cursor > max_nl_cursor)
- max_nl_cursor = cursor;
- cursor = vma->vm_end - vma->vm_start;
- if (cursor > max_nl_size)
- max_nl_size = cursor;
- }
-
- if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
- return SWAP_FAIL;
- }
-
- /*
- * We don't try to search for this page in the nonlinear vmas,
- * and page_referenced wouldn't have found it anyway. Instead
- * just walk the nonlinear vmas trying to age and unmap some.
- * The mapcount of the page we came in with is irrelevant,
- * but even so use it as a guide to how hard we should try?
- */
- mapcount = page_mapcount(page);
- if (!mapcount)
- return ret;
-
- cond_resched();
-
- max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
- if (max_nl_cursor == 0)
- max_nl_cursor = CLUSTER_SIZE;
-
- do {
- list_for_each_entry(vma,
- &mapping->i_mmap_nonlinear, shared.nonlinear) {
-
- cursor = (unsigned long) vma->vm_private_data;
- while (cursor < max_nl_cursor &&
- cursor < vma->vm_end - vma->vm_start) {
- if (try_to_unmap_cluster(cursor, &mapcount,
- vma, page) == SWAP_MLOCK)
- ret = SWAP_MLOCK;
- cursor += CLUSTER_SIZE;
- vma->vm_private_data = (void *) cursor;
- if ((int)mapcount <= 0)
- return ret;
- }
- vma->vm_private_data = (void *) max_nl_cursor;
- }
- cond_resched();
- max_nl_cursor += CLUSTER_SIZE;
- } while (max_nl_cursor <= max_nl_size);
-
- /*
- * Don't loop forever (perhaps all the remaining pages are
- * in locked vmas). Reset cursor on all unreserved nonlinear
- * vmas, now forgetting on which ones it had fallen behind.
- */
- list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.nonlinear)
- vma->vm_private_data = NULL;
-
- return ret;
-}
-
bool is_vma_temporary_stack(struct vm_area_struct *vma)
{
int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
@@ -1574,7 +1371,6 @@ int try_to_unmap(struct page *page, enum
.rmap_one = try_to_unmap_one,
.arg = (void *)flags,
.done = page_not_mapped,
- .file_nonlinear = try_to_unmap_nonlinear,
.anon_lock = page_lock_anon_vma_read,
};

@@ -1620,12 +1416,6 @@ int try_to_munlock(struct page *page)
.rmap_one = try_to_unmap_one,
.arg = (void *)TTU_MUNLOCK,
.done = page_not_mapped,
- /*
- * We don't bother to try to find the munlocked page in
- * nonlinears. It's costly. Instead, later, page reclaim logic
- * may call try_to_unmap() and recover PG_mlocked lazily.
- */
- .file_nonlinear = NULL,
.anon_lock = page_lock_anon_vma_read,

};
@@ -1753,14 +1543,6 @@ static int rmap_walk_file(struct page *p
goto done;
}

- if (!rwc->file_nonlinear)
- goto done;
-
- if (list_empty(&mapping->i_mmap_nonlinear))
- goto done;
-
- ret = rwc->file_nonlinear(page, mapping, rwc->arg);
-
done:
mutex_unlock(&mapping->i_mmap_mutex);
return ret;
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -1103,10 +1103,8 @@ void __init swap_setup(void)

if (bdi_init(swapper_spaces[0].backing_dev_info))
panic("Failed to init swap bdi");
- for (i = 0; i < MAX_SWAPFILES; i++) {
+ for (i = 0; i < MAX_SWAPFILES; i++)
spin_lock_init(&swapper_spaces[i].tree_lock);
- INIT_LIST_HEAD(&swapper_spaces[i].i_mmap_nonlinear);
- }
#endif

/* Use a smaller cluster for small-memory machines */