mm: optimize invalidation of shadow entries

The kernel invalidates the page cache in batches of PAGEVEC_SIZE.  For
each batch, it traverses the page cache tree and collects the entries
(folio and shadow entries) in the struct folio_batch.  For the shadow
entries present in the folio_batch, it has to traverse the page cache tree
for each individual entry to remove them.  This patch optimize this by
removing them in a single tree traversal.

To evaluate the changes, we created 200GiB file on a fuse fs and in a
memcg.  We created the shadow entries by triggering reclaim through
memory.reclaim in that specific memcg and measure the simple
fadvise(DONTNEED) operation.

 # time xfs_io -c 'fadvise -d 0 ${file_size}' file

              time (sec)
Without       5.12 +- 0.061
With-patch    4.19 +- 0.086 (18.16% decrease)

Link: https://lkml.kernel.org/r/20240925224716.2904498-3-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Chris Mason <clm@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/truncate.c b/mm/truncate.c
index 1d51c023d9c5a6cce9e38a7897cda2ee2f44b77e..520c8cf8f58f4ae218e4fabb3e0a4bfcc7f65876 100644 (file)
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -23,42 +23,28 @@
 #include <linux/rmap.h>
 #include "internal.h"
 
-/*
- * Regular page slots are stabilized by the page lock even without the tree
- * itself locked.  These unlocked entries need verification under the tree
- * lock.
- */
-static inline void __clear_shadow_entry(struct address_space *mapping,
-                               pgoff_t index, void *entry)
-{
-       XA_STATE(xas, &mapping->i_pages, index);
-
-       xas_set_update(&xas, workingset_update_node);
-       if (xas_load(&xas) != entry)
-               return;
-       xas_store(&xas, NULL);
-}
-
 static void clear_shadow_entries(struct address_space *mapping,
-                                struct folio_batch *fbatch, pgoff_t *indices)
+                                unsigned long start, unsigned long max)
 {
-       int i;
+       XA_STATE(xas, &mapping->i_pages, start);
+       struct folio *folio;
 
        /* Handled by shmem itself, or for DAX we do nothing. */
        if (shmem_mapping(mapping) || dax_mapping(mapping))
                return;
 
-       spin_lock(&mapping->host->i_lock);
-       xa_lock_irq(&mapping->i_pages);
+       xas_set_update(&xas, workingset_update_node);
 
-       for (i = 0; i < folio_batch_count(fbatch); i++) {
-               struct folio *folio = fbatch->folios[i];
+       spin_lock(&mapping->host->i_lock);
+       xas_lock_irq(&xas);
 
+       /* Clear all shadow entries from start to max */
+       xas_for_each(&xas, folio, max) {
                if (xa_is_value(folio))
-                       __clear_shadow_entry(mapping, indices[i], folio);
+                       xas_store(&xas, NULL);
        }
 
-       xa_unlock_irq(&mapping->i_pages);
+       xas_unlock_irq(&xas);
        if (mapping_shrinkable(mapping))
                inode_add_lru(mapping->host);
        spin_unlock(&mapping->host->i_lock);
@@ -481,7 +467,9 @@ unsigned long mapping_try_invalidate(struct address_space *mapping,
 
        folio_batch_init(&fbatch);
        while (find_lock_entries(mapping, &index, end, &fbatch, indices)) {
-               for (i = 0; i < folio_batch_count(&fbatch); i++) {
+               int nr = folio_batch_count(&fbatch);
+
+               for (i = 0; i < nr; i++) {
                        struct folio *folio = fbatch.folios[i];
 
                        /* We rely upon deletion not changing folio->index */
@@ -508,7 +496,7 @@ unsigned long mapping_try_invalidate(struct address_space *mapping,
                }
 
                if (xa_has_values)
-                       clear_shadow_entries(mapping, &fbatch, indices);
+                       clear_shadow_entries(mapping, indices[0], indices[nr-1]);
 
                folio_batch_remove_exceptionals(&fbatch);
                folio_batch_release(&fbatch);
@@ -612,7 +600,9 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
        folio_batch_init(&fbatch);
        index = start;
        while (find_get_entries(mapping, &index, end, &fbatch, indices)) {
-               for (i = 0; i < folio_batch_count(&fbatch); i++) {
+               int nr = folio_batch_count(&fbatch);
+
+               for (i = 0; i < nr; i++) {
                        struct folio *folio = fbatch.folios[i];
 
                        /* We rely upon deletion not changing folio->index */
@@ -658,7 +648,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
                }
 
                if (xa_has_values)
-                       clear_shadow_entries(mapping, &fbatch, indices);
+                       clear_shadow_entries(mapping, indices[0], indices[nr-1]);
 
                folio_batch_remove_exceptionals(&fbatch);
                folio_batch_release(&fbatch);