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From: Mel Gorman <mgorman@techsingularity.net>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Chuck Lever <chuck.lever@oracle.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Alexander Duyck <alexander.duyck@gmail.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux-Net <netdev@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>,
	Linux-NFS <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 4/9] mm/page_alloc: optimize code layout for __alloc_pages_bulk
Date: Thu, 25 Mar 2021 12:40:32 +0000	[thread overview]
Message-ID: <20210325124032.GR3697@techsingularity.net> (raw)
In-Reply-To: <20210325121217.GV1719932@casper.infradead.org>

On Thu, Mar 25, 2021 at 12:12:17PM +0000, Matthew Wilcox wrote:
> On Thu, Mar 25, 2021 at 11:42:23AM +0000, Mel Gorman wrote:
> >  
> > -	if (WARN_ON_ONCE(nr_pages <= 0))
> > +	if (unlikely(nr_pages <= 0))
> >  		return 0;
> 
> If we made nr_pages unsigned, we wouldn't need this check at all (ok,
> we'd still need to figure out what to do with 0).  But then, if a user
> inadvertently passes in -ENOMEM, we'll try to allocate 4 billion pages.

This is exactly why nr_pages is signed. An error in accounting by the
caller potentially puts the system under severe memory pressure. This
*should* only be a problem when a new caller of the API is being
implemented. The warning goes away in a later patch for reasons explained
in the changelog.

> So maybe we should check it.  Gah, API design is hard.

Yep.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2021-03-25 12:41 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-25 11:42 [PATCH 0/9 v6] Introduce a bulk order-0 page allocator with two in-tree users Mel Gorman
2021-03-25 11:42 ` [PATCH 1/9] mm/page_alloc: Rename alloced to allocated Mel Gorman
2021-03-25 11:59   ` Matthew Wilcox
2021-04-12 10:01   ` Vlastimil Babka
2021-03-25 11:42 ` [PATCH 2/9] mm/page_alloc: Add a bulk page allocator Mel Gorman
2021-03-25 12:05   ` Matthew Wilcox
2021-03-25 12:37     ` Mel Gorman
2021-04-12 10:21   ` Vlastimil Babka
2021-04-12 10:59     ` Mel Gorman
2021-04-12 11:19       ` Mel Gorman
2021-03-25 11:42 ` [PATCH 3/9] mm/page_alloc: Add an array-based interface to the " Mel Gorman
2021-04-12 10:36   ` Vlastimil Babka
2021-03-25 11:42 ` [PATCH 4/9] mm/page_alloc: optimize code layout for __alloc_pages_bulk Mel Gorman
2021-03-25 12:12   ` Matthew Wilcox
2021-03-25 12:40     ` Mel Gorman [this message]
2021-04-12 10:41   ` Vlastimil Babka
2021-03-25 11:42 ` [PATCH 5/9] mm/page_alloc: inline __rmqueue_pcplist Mel Gorman
2021-04-12 10:59   ` Vlastimil Babka
2021-03-25 11:42 ` [PATCH 6/9] SUNRPC: Set rq_page_end differently Mel Gorman
2021-03-25 11:42 ` [PATCH 7/9] SUNRPC: Refresh rq_pages using a bulk page allocator Mel Gorman
2021-03-25 11:42 ` [PATCH 8/9] net: page_pool: refactor dma_map into own function page_pool_dma_map Mel Gorman
2021-03-25 11:42 ` [PATCH 9/9] net: page_pool: use alloc_pages_bulk in refill code path Mel Gorman
2021-03-25 13:33   ` Alexander Lobakin
2021-03-25 12:50 ` [PATCH 0/9 v6] Introduce a bulk order-0 page allocator with two in-tree users Matthew Wilcox
2021-03-25 13:25   ` Mel Gorman
2021-03-25 14:06     ` Uladzislau Rezki
2021-03-25 14:09       ` Matthew Wilcox
2021-03-25 14:13         ` Uladzislau Rezki
2021-03-25 14:26       ` Mel Gorman
2021-03-25 14:46         ` Uladzislau Rezki

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