linux-kernel - Re: [PATCH v2 05/25] mm: Fix documentation of FGP flags

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Message-ID: <20200212191145.GH7778@bombadil.infradead.org>
Date:   Wed, 12 Feb 2020 11:11:45 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 05/25] mm: Fix documentation of FGP flags

On Tue, Feb 11, 2020 at 11:42:15PM -0800, Christoph Hellwig wrote:
> On Tue, Feb 11, 2020 at 08:18:25PM -0800, Matthew Wilcox wrote:
> > - * @fgp_flags: PCG flags
> > + * @fgp_flags: FGP flags
> >   * @gfp_mask: gfp mask to use for the page cache data page allocation
> >   *
> >   * Looks up the page cache slot at @mapping & @offset.
> >   *
> > - * PCG flags modify how the page is returned.
> > + * FGP flags modify how the page is returned.
> 
> This still looks weird.  Why not just a single line:
> 
> 	* @fgp_flags: FGP_* flags that control how the page is returned.

Well, now you got me reading the entire comment for this function, and
looking at the html output, so I ended up rewriting it entirely.

+++ b/mm/filemap.c
@@ -1574,37 +1574,34 @@ struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
 EXPORT_SYMBOL(find_lock_entry);
 
 /**
- * pagecache_get_page - find and get a page reference
- * @mapping: the address_space to search
- * @offset: the page index
- * @fgp_flags: FGP flags
- * @gfp_mask: gfp mask to use for the page cache data page allocation
- *
- * Looks up the page cache slot at @mapping & @offset.
+ * pagecache_get_page - Find and get a reference to a page.
+ * @mapping: The address_space to search.
+ * @offset: The page index.
+ * @fgp_flags: %FGP flags modify how the page is returned.
+ * @gfp_mask: Memory allocation flags to use if %FGP_CREAT is specified.
  *
- * FGP flags modify how the page is returned.
+ * Looks up the page cache entry at @mapping & @offset.
  *
- * @fgp_flags can be:
+ * @fgp_flags can be zero or more of these flags:
  *
- * - FGP_ACCESSED: the page will be marked accessed
- * - FGP_LOCK: Page is return locked
- * - FGP_CREAT: If page is not present then a new page is allocated using
- *   @gfp_mask and added to the page cache and the VM's LRU
- *   list. The page is returned locked and with an increased
- *   refcount.
- * - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do
- *   its own locking dance if the page is already in cache, or unlock the page
- *   before returning if we had to add the page to pagecache.
+ * * %FGP_ACCESSED - The page will be marked accessed.
+ * * %FGP_LOCK - The page is returned locked.
+ * * %FGP_CREAT - If no page is present then a new page is allocated using
+ *   @gfp_mask and added to the page cache and the VM's LRU list.
+ *   The page is returned locked and with an increased refcount.
+ * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
+ *   page is already in cache.  If the page was allocated, unlock it before
+ *   returning so the caller can do the same dance.
  *
- * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
- * if the GFP flags specified for FGP_CREAT are atomic.
+ * If %FGP_LOCK or %FGP_CREAT are specified then the function may sleep even
+ * if the %GFP flags specified for %FGP_CREAT are atomic.
  *
  * If there is a page cache page, it is returned with an increased refcount.
  *
- * Return: the found page or %NULL otherwise.
+ * Return: The found page or %NULL otherwise.
  */
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
-       int fgp_flags, gfp_t gfp_mask)
+               int fgp_flags, gfp_t gfp_mask)
 {