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Message-ID: <133cd73f-3080-4362-bc3e-ef4cc8880a20@infradead.org>
Date: Thu, 4 Jan 2024 13:06:10 -0800
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Subject: Re: [PATCH 2/5] buffer: Add kernel-doc for block_dirty_folio()
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To: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
 Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240104163652.3705753-1-willy@infradead.org>
 <20240104163652.3705753-3-willy@infradead.org>
From: Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <20240104163652.3705753-3-willy@infradead.org>
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On 1/4/24 08:36, Matthew Wilcox (Oracle) wrote:
> Turn the excellent documentation for this function into kernel-doc.
> Replace 'page' with 'folio' and make a few other minor updates.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  fs/buffer.c | 54 +++++++++++++++++++++++++++++------------------------
>  1 file changed, 30 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 5c29850e4781..31e171382e00 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -687,30 +687,36 @@ void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
>  }
>  EXPORT_SYMBOL(mark_buffer_dirty_inode);
>  
> -/*
> - * Add a page to the dirty page list.
> - *
> - * It is a sad fact of life that this function is called from several places
> - * deeply under spinlocking.  It may not sleep.
> - *
> - * If the page has buffers, the uptodate buffers are set dirty, to preserve
> - * dirty-state coherency between the page and the buffers.  It the page does
> - * not have buffers then when they are later attached they will all be set
> - * dirty.
> - *
> - * The buffers are dirtied before the page is dirtied.  There's a small race
> - * window in which a writepage caller may see the page cleanness but not the
> - * buffer dirtiness.  That's fine.  If this code were to set the page dirty
> - * before the buffers, a concurrent writepage caller could clear the page dirty
> - * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
> - * page on the dirty page list.
> - *
> - * We use private_lock to lock against try_to_free_buffers while using the
> - * page's buffer list.  Also use this to protect against clean buffers being
> - * added to the page after it was set dirty.
> - *
> - * FIXME: may need to call ->reservepage here as well.  That's rather up to the
> - * address_space though.
> +/**
> + * block_dirty_folio - Mark a folio as dirty.
> + * @mapping: The address space containing this folio.
> + * @folio: The folio to mark dirty.
> + *
> + * Filesystems which use buffer_heads can use this function as their
> + * ->dirty_folio implementation.  Some filesystems need to do a little
> + * work before calling this function.  Filesystems which do not use
> + * buffer_heads should call filemap_dirty_folio() instead.
> + *
> + * If the folio has buffers, the uptodate buffers are set dirty, to
> + * preserve dirty-state coherency between the folio and the buffers.
> + * It the folio does not have buffers then when they are later attached
> + * they will all be set dirty.
> + *
> + * The buffers are dirtied before the folio is dirtied.  There's a small
> + * race window in which writeback may see the folio cleanness but not the
> + * buffer dirtiness.  That's fine.  If this code were to set the folio
> + * dirty before the buffers, writeback could clear the folio dirty flag,
> + * see a bunch of clean buffers and we'd end up with dirty buffers/clean
> + * folio on the dirty folio list.
> + *
> + * We use private_lock to lock against try_to_free_buffers() while
> + * using the folio's buffer list.  This also prevents clean buffers
> + * being added to the folio after it was set dirty.
> + *
> + * Context: May only be called from process context.  Does not sleep.
> + * Caller must ensure that @folio cannot be truncated during this call,
> + * typically by holding the folio lock or having a page in the folio
> + * mapped and holding the page table lock.

 * Return: tbd

?

>   */
>  bool block_dirty_folio(struct address_space *mapping, struct folio *folio)
>  {

-- 
#Randy