anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
if (anon_vma) {
atomic_set(&anon_vma->refcount, 1);
+ anon_vma->degree = 1; /* Reference for first vma */
+ anon_vma->parent = anon_vma;
/*
* Initialise the anon_vma root to point to itself. If called
* from fork, the root will be reset to the parents anon_vma.
if (likely(!vma->anon_vma)) {
vma->anon_vma = anon_vma;
anon_vma_chain_link(vma, avc, anon_vma);
+ /* vma reference or self-parent link for new root */
+ anon_vma->degree++;
allocated = NULL;
avc = NULL;
}
/*
* Attach the anon_vmas from src to dst.
* Returns 0 on success, -ENOMEM on failure.
+ *
+ * If dst->anon_vma is NULL this function tries to find and reuse existing
+ * anon_vma which has no vmas and only one child anon_vma. This prevents
+ * degradation of anon_vma hierarchy to endless linear chain in case of
+ * constantly forking task. On the other hand, an anon_vma with more than one
+ * child isn't reused even if there was no alive vma, thus rmap walker has a
+ * good chance of avoiding scanning the whole hierarchy when it searches where
+ * page is mapped.
*/
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
anon_vma = pavc->anon_vma;
root = lock_anon_vma_root(root, anon_vma);
anon_vma_chain_link(dst, avc, anon_vma);
+
+ /*
+ * Reuse existing anon_vma if its degree lower than two,
+ * that means it has no vma and only one anon_vma child.
+ *
+ * Do not chose parent anon_vma, otherwise first child
+ * will always reuse it. Root anon_vma is never reused:
+ * it has self-parent reference and at least one child.
+ */
+ if (!dst->anon_vma && anon_vma != src->anon_vma &&
+ anon_vma->degree < 2)
+ dst->anon_vma = anon_vma;
}
+ if (dst->anon_vma)
+ dst->anon_vma->degree++;
unlock_anon_vma_root(root);
return 0;
if (!pvma->anon_vma)
return 0;
+ /* Drop inherited anon_vma, we'll reuse existing or allocate new. */
+ vma->anon_vma = NULL;
+
/*
* First, attach the new VMA to the parent VMA's anon_vmas,
* so rmap can find non-COWed pages in child processes.
if (error)
return error;
+ /* An existing anon_vma has been reused, all done then. */
+ if (vma->anon_vma)
+ return 0;
+
/* Then add our own anon_vma. */
anon_vma = anon_vma_alloc();
if (!anon_vma)
* lock any of the anon_vmas in this anon_vma tree.
*/
anon_vma->root = pvma->anon_vma->root;
+ anon_vma->parent = pvma->anon_vma;
/*
* With refcounts, an anon_vma can stay around longer than the
* process it belongs to. The root anon_vma needs to be pinned until
vma->anon_vma = anon_vma;
anon_vma_lock_write(anon_vma);
anon_vma_chain_link(vma, avc, anon_vma);
+ anon_vma->parent->degree++;
anon_vma_unlock_write(anon_vma);
return 0;
* Leave empty anon_vmas on the list - we'll need
* to free them outside the lock.
*/
- if (RB_EMPTY_ROOT(&anon_vma->rb_root))
+ if (RB_EMPTY_ROOT(&anon_vma->rb_root)) {
+ anon_vma->parent->degree--;
continue;
+ }
list_del(&avc->same_vma);
anon_vma_chain_free(avc);
}
+ if (vma->anon_vma)
+ vma->anon_vma->degree--;
unlock_anon_vma_root(root);
/*
list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
struct anon_vma *anon_vma = avc->anon_vma;
+ BUG_ON(anon_vma->degree);
put_anon_vma(anon_vma);
list_del(&avc->same_vma);
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;
void page_add_file_rmap(struct page *page)
{
struct mem_cgroup *memcg;
- unsigned long flags;
- bool locked;
- memcg = mem_cgroup_begin_page_stat(page, &locked, &flags);
+ memcg = mem_cgroup_begin_page_stat(page);
if (atomic_inc_and_test(&page->_mapcount)) {
__inc_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_inc_page_stat(memcg, MEM_CGROUP_STAT_FILE_MAPPED);
}
- mem_cgroup_end_page_stat(memcg, &locked, &flags);
+ mem_cgroup_end_page_stat(memcg);
}
static void page_remove_file_rmap(struct page *page)
{
struct mem_cgroup *memcg;
- unsigned long flags;
- bool locked;
- memcg = mem_cgroup_begin_page_stat(page, &locked, &flags);
+ memcg = mem_cgroup_begin_page_stat(page);
/* page still mapped by someone else? */
if (!atomic_add_negative(-1, &page->_mapcount))
if (unlikely(PageMlocked(page)))
clear_page_mlock(page);
out:
- mem_cgroup_end_page_stat(memcg, &locked, &flags);
+ mem_cgroup_end_page_stat(memcg);
}
/**
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 */
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 */
- }
-
- /*
- * No need for _notify because we're within an
- * mmu_notifier_invalidate_range_ {start|end} scope.
- */
- if (ptep_clear_flush_young(vma, address, pte))
- continue;
-
- /* Nuke the page table entry. */
- flush_cache_page(vma, address, pte_pfn(*pte));
- pteval = ptep_clear_flush_notify(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);
.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,
};
.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,
};
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:
i_mmap_unlock_read(mapping);
return ret;
projects / firefly-linux-kernel-4.4.55.git / blobdiff