Re: [Virtio-fs] [PATCH v3 2/3] dax: Add a wakeup mode parameter to put_unlocked_entry()

[Greg Kurz]

On Mon, 19 Apr 2021 17:36:35 -0400
Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:

> As of now put_unlocked_entry() always wakes up next waiter. In next
> patches we want to wake up all waiters at one callsite. Hence, add a
> parameter to the function.
> 
> This patch does not introduce any change of behavior.
> 
> Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
>  fs/dax.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 00978d0838b1..f19d76a6a493 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -275,11 +275,12 @@ static void wait_entry_unlocked(struct xa_state *xas, void *entry)
>  	finish_wait(wq, &ewait.wait);
>  }
>  
> -static void put_unlocked_entry(struct xa_state *xas, void *entry)
> +static void put_unlocked_entry(struct xa_state *xas, void *entry,
> +			       enum dax_entry_wake_mode mode)
>  {
>  	/* If we were the only waiter woken, wake the next one */

With this change, the comment is no longer accurate since the
function can now wake all waiters if passed mode == WAKE_ALL.
Also, it paraphrases the code which is simple enough, so I'd
simply drop it.

This is minor though and it shouldn't prevent this fix to go
forward.

Reviewed-by: Greg Kurz <groug@xxxxxxxx>

>  	if (entry && !dax_is_conflict(entry))
> -		dax_wake_entry(xas, entry, WAKE_NEXT);
> +		dax_wake_entry(xas, entry, mode);
>  }
>  
>  /*
> @@ -633,7 +634,7 @@ struct page *dax_layout_busy_page_range(struct address_space *mapping,
>  			entry = get_unlocked_entry(&xas, 0);
>  		if (entry)
>  			page = dax_busy_page(entry);
> -		put_unlocked_entry(&xas, entry);
> +		put_unlocked_entry(&xas, entry, WAKE_NEXT);
>  		if (page)
>  			break;
>  		if (++scanned % XA_CHECK_SCHED)
> @@ -675,7 +676,7 @@ static int __dax_invalidate_entry(struct address_space *mapping,
>  	mapping->nrexceptional--;
>  	ret = 1;
>  out:
> -	put_unlocked_entry(&xas, entry);
> +	put_unlocked_entry(&xas, entry, WAKE_NEXT);
>  	xas_unlock_irq(&xas);
>  	return ret;
>  }
> @@ -954,7 +955,7 @@ static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
>  	return ret;
>  
>   put_unlocked:
> -	put_unlocked_entry(xas, entry);
> +	put_unlocked_entry(xas, entry, WAKE_NEXT);
>  	return ret;
>  }
>  
> @@ -1695,7 +1696,7 @@ dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn, unsigned int order)
>  	/* Did we race with someone splitting entry or so? */
>  	if (!entry || dax_is_conflict(entry) ||
>  	    (order == 0 && !dax_is_pte_entry(entry))) {
> -		put_unlocked_entry(&xas, entry);
> +		put_unlocked_entry(&xas, entry, WAKE_NEXT);
>  		xas_unlock_irq(&xas);
>  		trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
>  						      VM_FAULT_NOPAGE);