Re: [PATCH v2 3/3] fbdev: Refactor implementation of page_mkwrite

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 25.04.22 um 20:24 schrieb Sam Ravnborg:
> Hi Thomas.
> 
> On Mon, Apr 25, 2022 at 01:27:51PM +0200, Thomas Zimmermann wrote:
>> Refactor the page-write handler for deferred I/O. Drivers use the
>> function to let fbdev track written pages of mmap'ed framebuffer
>> memory.
> 
> I like how the comments got a brush up and a little more info was added.
> But I do not see the point of the refactoring - the code is equally
> readable before and after - maybe even easier before (modulus the
> improved comments).

FYI I'm going to move the locking into the track-page helper, which 
makes the code more readable.

Best regards
Thomas

> 
> But if you consider it better keep it. Again just my thoughts when
> reading the code.
> 
> 	Sam
> 
>>
>> v2:
>> 	* don't export the helper until we have an external caller
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
>> ---
>>   drivers/video/fbdev/core/fb_defio.c | 68 ++++++++++++++++++++---------
>>   1 file changed, 48 insertions(+), 20 deletions(-)
>>
>> diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
>> index a03b9c64fc61..214581ce5840 100644
>> --- a/drivers/video/fbdev/core/fb_defio.c
>> +++ b/drivers/video/fbdev/core/fb_defio.c
>> @@ -143,29 +143,18 @@ int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasy
>>   }
>>   EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);
>>   
>> -/* vm_ops->page_mkwrite handler */
>> -static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
>> +/*
>> + * Adds a page to the dirty list. Requires caller to hold
>> + * struct fb_deferred_io.lock. Call this from struct
>> + * vm_operations_struct.page_mkwrite.
>> + */
>> +static vm_fault_t __fb_deferred_io_track_page(struct fb_info *info, unsigned long offset,
>> +					      struct page *page)
>>   {
>> -	struct page *page = vmf->page;
>> -	struct fb_info *info = vmf->vma->vm_private_data;
>>   	struct fb_deferred_io *fbdefio = info->fbdefio;
>>   	struct fb_deferred_io_pageref *pageref;
>> -	unsigned long offset;
>>   	vm_fault_t ret;
>>   
>> -	offset = (vmf->address - vmf->vma->vm_start);
>> -
>> -	/* this is a callback we get when userspace first tries to
>> -	write to the page. we schedule a workqueue. that workqueue
>> -	will eventually mkclean the touched pages and execute the
>> -	deferred framebuffer IO. then if userspace touches a page
>> -	again, we repeat the same scheme */
>> -
>> -	file_update_time(vmf->vma->vm_file);
>> -
>> -	/* protect against the workqueue changing the page list */
>> -	mutex_lock(&fbdefio->lock);
>> -
>>   	/* first write in this cycle, notify the driver */
>>   	if (fbdefio->first_io && list_empty(&fbdefio->pagelist))
>>   		fbdefio->first_io(info);
>> @@ -186,8 +175,6 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
>>   	 */
>>   	lock_page(pageref->page);
>>   
>> -	mutex_unlock(&fbdefio->lock);
>> -
>>   	/* come back after delay to process the deferred IO */
>>   	schedule_delayed_work(&info->deferred_work, fbdefio->delay);
>>   	return VM_FAULT_LOCKED;
>> @@ -197,6 +184,47 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
>>   	return ret;
>>   }
>>   
>> +/*
>> + * fb_deferred_io_page_mkwrite - Mark a page as written for deferred I/O
>> + * @fb_info: The fbdev info structure
>> + * @vmf: The VM fault
>> + *
>> + * This is a callback we get when userspace first tries to
>> + * write to the page. We schedule a workqueue. That workqueue
>> + * will eventually mkclean the touched pages and execute the
>> + * deferred framebuffer IO. Then if userspace touches a page
>> + * again, we repeat the same scheme.
>> + *
>> + * Returns:
>> + * VM_FAULT_LOCKED on success, or a VM_FAULT error otherwise.
>> + */
>> +static vm_fault_t fb_deferred_io_page_mkwrite(struct fb_info *info, struct vm_fault *vmf)
>> +{
>> +	struct page *page = vmf->page;
>> +	struct fb_deferred_io *fbdefio = info->fbdefio;
>> +	unsigned long offset;
>> +	vm_fault_t ret;
>> +
>> +	offset = (vmf->address - vmf->vma->vm_start);
>> +
>> +	file_update_time(vmf->vma->vm_file);
>> +
>> +	/* protect against the workqueue changing the page list */
>> +	mutex_lock(&fbdefio->lock);
>> +	ret = __fb_deferred_io_track_page(info, offset, page);
>> +	mutex_unlock(&fbdefio->lock);
>> +
>> +	return ret;
>> +}
>> +
>> +/* vm_ops->page_mkwrite handler */
>> +static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
>> +{
>> +	struct fb_info *info = vmf->vma->vm_private_data;
>> +
>> +	return fb_deferred_io_page_mkwrite(info, vmf);
>> +}
>> +
>>   static const struct vm_operations_struct fb_deferred_io_vm_ops = {
>>   	.fault		= fb_deferred_io_fault,
>>   	.page_mkwrite	= fb_deferred_io_mkwrite,
>> -- 
>> 2.36.0

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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