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author | Matthew Wilcox (Oracle) <willy@infradead.org> | 2021-05-10 16:33:22 -0400 |
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committer | Matthew Wilcox (Oracle) <willy@infradead.org> | 2021-09-27 09:27:29 -0400 |
commit | 020853b6f5ead2849b055e9873ff7267ce584256 (patch) | |
tree | 12095453d223c93b1de1aec6560704972eaf88fe /mm/filemap.c | |
parent | 86d234cb0499c6466ccfc45f6501bc0cd4621c60 (diff) | |
download | linux-020853b6f5ead2849b055e9873ff7267ce584256.tar.bz2 |
mm: Add folio_try_get_rcu()
This is the equivalent of page_cache_get_speculative(). Also add
folio_ref_try_add_rcu (the equivalent of page_cache_add_speculative)
and folio_get_unless_zero() (the equivalent of get_page_unless_zero()).
The new kernel-doc attempts to explain from the user's point of view
when to use folio_try_get_rcu() and when to use folio_get_unless_zero(),
because there seems to be some confusion currently between the users of
page_cache_get_speculative() and get_page_unless_zero().
Reimplement page_cache_add_speculative() and page_cache_get_speculative()
as wrappers around the folio equivalents, but leave get_page_unless_zero()
alone for now. This commit reduces text size by 3 bytes due to slightly
different register allocation & instruction selections.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
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. |