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page cache: Convert filemap_map_pages to XArray 

Slight change of strategy here; if we have trouble getting hold of a
page for whatever reason (eg a compound page is split underneath us),
don't spin to stabilise the page, just continue the iteration, like we
would if we failed to trylock the page.  Since this is a speculative
optimisation, it feels like we should allow the process to take an extra
fault if it turns out to need this page instead of spending time to pin
down a page it may not need.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
This commit is contained in:
Matthew Wilcox 2018-05-17 00:08:30 -04:00
parent c1901cd33c
commit 070e807c69
1 changed files with 13 additions and 29 deletions
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42
mm/filemap.c
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@ -2516,45 +2516,31 @@ EXPORT_SYMBOL(filemap_fault);
void filemap_map_pages(struct vm_fault *vmf,
pgoff_t start_pgoff, pgoff_t end_pgoff)
{
struct radix_tree_iter iter;
void **slot;
struct file *file = vmf->vma->vm_file;
struct address_space *mapping = file->f_mapping;
pgoff_t last_pgoff = start_pgoff;
unsigned long max_idx;
XA_STATE(xas, &mapping->i_pages, start_pgoff);
struct page *head, *page;
rcu_read_lock();
radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start_pgoff) {
if (iter.index > end_pgoff)
break;
repeat:
page = radix_tree_deref_slot(slot);
if (unlikely(!page))
xas_for_each(&xas, page, end_pgoff) {
if (xas_retry(&xas, page))
continue;
if (xa_is_value(page))
goto next;
if (radix_tree_exception(page)) {
if (radix_tree_deref_retry(page)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
goto next;
}
head = compound_head(page);
if (!page_cache_get_speculative(head))
goto repeat;
goto next;
/* The page was split under us? */
if (compound_head(page) != head) {
put_page(head);
goto repeat;
}
if (compound_head(page) != head)
goto skip;
/* Has the page moved? */
if (unlikely(page != *slot)) {
put_page(head);
goto repeat;
}
if (unlikely(page != xas_reload(&xas)))
goto skip;
if (!PageUptodate(page) ||
PageReadahead(page) ||
@ -2573,10 +2559,10 @@ repeat:
if (file->f_ra.mmap_miss > 0)
file->f_ra.mmap_miss--;
vmf->address += (iter.index - last_pgoff) << PAGE_SHIFT;
vmf->address += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
if (vmf->pte)
vmf->pte += iter.index - last_pgoff;
last_pgoff = iter.index;
vmf->pte += xas.xa_index - last_pgoff;
last_pgoff = xas.xa_index;
if (alloc_set_pte(vmf, NULL, page))
goto unlock;
unlock_page(page);
@ -2589,8 +2575,6 @@ next:
/* Huge page is mapped? No need to proceed. */
if (pmd_trans_huge(*vmf->pmd))
break;
if (iter.index == end_pgoff)
break;
}
rcu_read_unlock();
}