diff options
Diffstat (limited to 'mm/filemap.c')
| -rw-r--r-- | mm/filemap.c | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index dae481293b5d..9fcc3d94cfcd 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1802,6 +1802,26 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping, EXPORT_SYMBOL(page_cache_prev_miss); /* + * Lockless page cache protocol: + * On the lookup side: + * 1. Load the folio from i_pages + * 2. Increment the refcount if it's not zero + * 3. If the folio is not found by xas_reload(), put the refcount and retry + * + * On the removal side: + * A. Freeze the page (by zeroing the refcount if nobody else has a reference) + * B. Remove the page from i_pages + * C. Return the page to the page allocator + * + * This means that any page may have its reference count temporarily + * increased by a speculative page cache (or fast GUP) lookup as it can + * be allocated by another user before the RCU grace period expires. + * Because the refcount temporarily acquired here may end up being the + * last refcount on the page, any page allocation must be freeable by + * folio_put(). + */ + +/* * mapping_get_entry - Get a page cache entry. * @mapping: the address_space to search * @index: The page cache index. |