[patch 049/262] mm: move more expensive part of XA setup out of mapping check

Andrew Morton
2021-11-05T20:37:16Z

From: Jens Axboe <axboe@kernel.dk>
Subject: mm: move more expensive part of XA setup out of mapping check

The fast path here is not needing any writeback, yet we spend time setting
up the xarray lookup data upfront. Move the part that actually needs to
iterate the address space mapping into a separate helper, saving ~30% of
the time here.

Link: https://lkml.kernel.org/r/49f67983-b802-8929-edab-d807f745c9ca@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/filemap.c | 43 +++++++++++++++++++++++++------------------
1 file changed, 25 insertions(+), 18 deletions(-)

--- a/mm/filemap.c~mm-move-more-expensive-part-of-xa-setup-out-of-mapping-check
+++ a/mm/filemap.c
@@ -639,6 +639,30 @@ static bool mapping_needs_writeback(stru
return mapping->nrpages;
}

+static bool filemap_range_has_writeback(struct address_space *mapping,
+ loff_t start_byte, loff_t end_byte)
+{
+ XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+ pgoff_t max = end_byte >> PAGE_SHIFT;
+ struct page *page;
+
+ if (end_byte < start_byte)
+ return false;
+
+ rcu_read_lock();
+ xas_for_each(&xas, page, max) {
+ if (xas_retry(&xas, page))
+ continue;
+ if (xa_is_value(page))
+ continue;
+ if (PageDirty(page) || PageLocked(page) || PageWriteback(page))
+ break;
+ }
+ rcu_read_unlock();
+ return page != NULL;
+
+}
+
/**
* filemap_range_needs_writeback - check if range potentially needs writeback
* @mapping: address space within which to check
@@ -656,29 +680,12 @@ static bool mapping_needs_writeback(stru
bool filemap_range_needs_writeback(struct address_space *mapping,
loff_t start_byte, loff_t end_byte)
{
- XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
- pgoff_t max = end_byte >> PAGE_SHIFT;
- struct page *page;
-
if (!mapping_needs_writeback(mapping))
return false;
if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
return false;
- if (end_byte < start_byte)
- return false;
-
- rcu_read_lock();
- xas_for_each(&xas, page, max) {
- if (xas_retry(&xas, page))
- continue;
- if (xa_is_value(page))
- continue;
- if (PageDirty(page) || PageLocked(page) || PageWriteback(page))
- break;
- }
- rcu_read_unlock();
- return page != NULL;
+ return filemap_range_has_writeback(mapping, start_byte, end_byte);
}
EXPORT_SYMBOL_GPL(filemap_range_needs_writeback);

_