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From:   "Wang, Wei W" <wei.w.wang@intel.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Jason Wang <jasowang@redhat.com>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: RE: [PATCH v3 2/2] balloon: fix up comments
Thread-Topic: [PATCH v3 2/2] balloon: fix up comments
Thread-Index: AQHVPWPB7Kn6mp4V4ECCoWD/TZ2+lqbQWhSw
Date:   Thu, 18 Jul 2019 13:47:40 +0000
Message-ID: <286AC319A985734F985F78AFA26841F73E1705ED@shsmsx102.ccr.corp.intel.com>
References: <20190718122324.10552-1-mst@redhat.com>
 <20190718122324.10552-2-mst@redhat.com>
In-Reply-To: <20190718122324.10552-2-mst@redhat.com>
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On Thursday, July 18, 2019 8:24 PM, Michael S. Tsirkin wrote:
>  /*
>   * balloon_page_alloc - allocates a new page for insertion into the balloon
> - *			  page list.
> + *			page list.
>   *
> - * Driver must call it to properly allocate a new enlisted balloon page.
> - * Driver must call balloon_page_enqueue before definitively removing it
> from
> - * the guest system.  This function returns the page address for the recently
> - * allocated page or NULL in the case we fail to allocate a new page this turn.
> + * Driver must call this function to properly allocate a new enlisted balloon
> page.

Probably better to say "allocate a new balloon page to enlist" ?
"enlisted page" implies that the allocated page has been added to the list, which might
be misleading.


> + * Driver must call balloon_page_enqueue before definitively removing
> + the page
> + * from the guest system.
> + *
> + * Returns: struct page address for the allocated page or NULL in case it fails
> + * 			to allocate a new page.
>   */

Returns: pointer to the page struct of the allocated page, or NULL if allocation fails.


>  struct page *balloon_page_alloc(void)
>  {
> @@ -130,19 +133,15 @@ EXPORT_SYMBOL_GPL(balloon_page_alloc);
>  /*
>   * balloon_page_enqueue - inserts a new page into the balloon page list.
>   *
> - * @b_dev_info: balloon device descriptor where we will insert a new page
> to
> + * @b_dev_info: balloon device descriptor where we will insert a new
> + page
>   * @page: new page to enqueue - allocated using balloon_page_alloc.
>   *
> - * Driver must call it to properly enqueue a new allocated balloon page
> - * before definitively removing it from the guest system.
> + * Drivers must call this function to properly enqueue a new allocated
> + balloon
> + * page before definitively removing the page from the guest system.
>   *
> - * Drivers must not call balloon_page_enqueue on pages that have been
> - * pushed to a list with balloon_page_push before removing them with
> - * balloon_page_pop. To all pages on a list, use balloon_page_list_enqueue
> - * instead.
> - *
> - * This function returns the page address for the recently enqueued page or
> - * NULL in the case we fail to allocate a new page this turn.
> + * Drivers must not call balloon_page_enqueue on pages that have been
> + pushed to
> + * a list with balloon_page_push before removing them with
> + balloon_page_pop. To
> + * enqueue all pages on a list, use balloon_page_list_enqueue instead.

"To enqueue a list of pages" ?


>   */
>  void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
>  			  struct page *page)
> @@ -157,14 +156,24 @@ EXPORT_SYMBOL_GPL(balloon_page_enqueue);
> 
>  /*
>   * balloon_page_dequeue - removes a page from balloon's page list and
> returns
> - *			  the its address to allow the driver release the page.
> + *			  its address to allow the driver to release the page.
>   * @b_dev_info: balloon device decriptor where we will grab a page from.
>   *
> - * Driver must call it to properly de-allocate a previous enlisted balloon
> page
> - * before definetively releasing it back to the guest system.
> - * This function returns the page address for the recently dequeued page or
> - * NULL in the case we find balloon's page list temporarily empty due to
> - * compaction isolated pages.
> + * Driver must call this to properly dequeue a previously enqueued page
 
"call this function"?
 

> + * before definitively releasing it back to the guest system.
> + *
> + * Caller must perform its own accounting to ensure that this
> + * function is called only if some pages are actually enqueued.


"only when" ?

> + *
> + * Note that this function may fail to dequeue some pages even if there

"even when" ?

> + are
> + * some enqueued pages - since the page list can be temporarily empty
> + due to
> + * the compaction of isolated pages.
> + *
> + * TODO: remove the caller accounting requirements, and allow caller to
> + wait
> + * until all pages can be dequeued.
> + *
> + * Returns: struct page address for the dequeued page, or NULL if it fails to
> + * 			dequeue any pages.

Returns: pointer to the page struct of the dequeued page, or NULL if no page gets dequeued.


>   */
>  struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
> { @@ -177,9 +186,9 @@ struct page *balloon_page_dequeue(struct
> balloon_dev_info *b_dev_info)
>  	if (n_pages != 1) {
>  		/*
>  		 * If we are unable to dequeue a balloon page because the
> page
> -		 * list is empty and there is no isolated pages, then
> something
> +		 * list is empty and there are no isolated pages, then
> something
>  		 * went out of track and some balloon pages are lost.
> -		 * BUG() here, otherwise the balloon driver may get stuck
> into
> +		 * BUG() here, otherwise the balloon driver may get stuck in
>  		 * an infinite loop while attempting to release all its pages.
>  		 */
>  		spin_lock_irqsave(&b_dev_info->pages_lock, flags); @@ -
> 230,8 +239,8 @@ int balloon_page_migrate(struct address_space *mapping,
> 
>  	/*
>  	 * We can not easily support the no copy case here so ignore it as it
 
"cannot"

> -	 * is unlikely to be use with ballon pages. See include/linux/hmm.h
> for
> -	 * user of the MIGRATE_SYNC_NO_COPY mode.
> +	 * is unlikely to be used with ballon pages. See include/linux/hmm.h


"ballon" -> "balloon"


> for
> +	 * a user of the MIGRATE_SYNC_NO_COPY mode.

"for the usage of" ?


Other parts look good to me.
Reviewed-by: Wei Wang <wei.w.wang@intel.com>

Best,
Wei