From: Mike Rapoport <rppt@linux.ibm.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Nick Piggin <npiggin@gmail.com>, Hugh Dickins <hughd@google.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org, hch@lst.de,
rdunlap@infradead.org
Subject: Re: [PATCH v2] page_alloc: Fix freeing non-compound pages
Date: Wed, 30 Sep 2020 12:17:55 +0300 [thread overview]
Message-ID: <20200930091755.GB3226834@linux.ibm.com> (raw)
In-Reply-To: <20200929140622.GE20115@casper.infradead.org>
On Tue, Sep 29, 2020 at 03:06:22PM +0100, Matthew Wilcox wrote:
> On Tue, Sep 29, 2020 at 10:26:22AM +0300, Mike Rapoport wrote:
> > This sentence presumes existing description/prior knowledge about
> > put_page().
> >
> > Maybe
> >
> > This function can free multi-page allocations that were not allocated
> > with %__GFP_COMP, unlike put_page() that would free only the first page
> > in such case. __free_pages() does not ...
>
> Thanks. After waking up this morning I did a more extensive rewrite:
I like this one
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
> /**
> * __free_pages - Free pages allocated with alloc_pages().
> * @page: The page pointer returned from alloc_pages().
> * @order: The order of the allocation.
> *
> * This function can free multi-page allocations that are not compound
> * pages. It does not check that the @order passed in matches that of
> * the allocation, so it is easy to leak memory. Freeing more memory
> * than was allocated will probably emit a warning.
> *
> * If the last reference to this page is speculative, it will be released
> * by put_page() which only frees the first page of a non-compound
> * allocation. To prevent the remaining pages from being leaked, we free
> * the subsequent pages here. If you want to use the page's reference
> * count to decide when to free the allocation, you should allocate a
> * compound page, and use put_page() instead of __free_pages().
> *
> * Context: May be called in interrupt context or holding a normal
> * spinlock, but not in NMI context or while holding a raw spinlock.
> */
>
--
Sincerely yours,
Mike.
prev parent reply other threads:[~2020-09-30 9:18 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-26 21:39 [PATCH v2] page_alloc: Fix freeing non-compound pages Matthew Wilcox (Oracle)
2020-09-29 1:03 ` Andrew Morton
2020-09-29 1:17 ` Matthew Wilcox
2020-09-29 4:46 ` Andrew Morton
2020-09-29 22:53 ` Matthew Wilcox
2020-10-19 1:00 ` Nicholas Piggin
2020-09-29 3:40 ` Matthew Wilcox
2020-09-29 7:26 ` Mike Rapoport
2020-09-29 14:06 ` Matthew Wilcox
2020-09-30 9:17 ` Mike Rapoport [this message]
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