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Date:   Tue, 29 Jun 2021 16:33:49 +0100
From:   Mel Gorman <mgorman@techsingularity.net>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     linux-nfs@vger.kernel.org, linux-mm@kvack.org, brouer@redhat.com
Subject: Re: [PATCH v3] mm/page_alloc: Further fix __alloc_pages_bulk()
 return value
Message-ID: <20210629153349.GG3840@techsingularity.net>
References: <162497449506.16614.7781489905877008435.stgit@klimt.1015granger.net>
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On Tue, Jun 29, 2021 at 09:48:15AM -0400, Chuck Lever wrote:
> The author of commit b3b64ebd3822 ("mm/page_alloc: do bulk array
> bounds check after checking populated elements") was possibly
> confused by the mixture of return values throughout the function.
> 
> The API contract is clear that the function "Returns the number of
> pages on the list or array." It does not list zero as a unique
> return value with a special meaning. Therefore zero is a plausible
> return value only if @nr_pages is zero or less.
> 
> Clean up the return logic to make it clear that the returned value
> is always the total number of pages in the array/list, not the
> number of pages that were allocated during this call.
> 
> The only change in behavior with this patch is the value returned
> if prepare_alloc_pages() fails. To match the API contract, the
> number of pages currently in the array/list is returned in this
> case.
> 
> The call site in __page_pool_alloc_pages_slow() also seems to be
> confused on this matter. It should be attended to by someone who
> is familiar with that code.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs