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: Tue, 29 Sep 2020 10:26:22 +0300 [thread overview]
Message-ID: <20200929072622.GN2645148@linux.ibm.com> (raw)
In-Reply-To: <20200929034026.GA20115@casper.infradead.org>
On Tue, Sep 29, 2020 at 04:40:26AM +0100, Matthew Wilcox wrote:
> On Mon, Sep 28, 2020 at 06:03:07PM -0700, Andrew Morton wrote:
> > Well that's weird and scary looking. `page' has non-zero refcount yet
> > we go and free random followon pages. Methinks it merits an
> > explanatory comment?
>
> Here's some kernel-doc. Opinions?
>
> /**
> * __free_pages - Free pages allocated with alloc_pages().
> * @page: The page pointer returned from alloc_pages().
> * @order: The order of the allocation.
> *
> * This function differs from put_page() in that it can free multi-page
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 ...
> * allocations that were not allocated with %__GFP_COMP. This function
> * does not check that the @order passed in matches that of the
> * allocation, so it is possible to leak memory. Freeing more memory than
> * was allocated will probably be warned about by other debugging checks.
> *
> * It is only safe to use the page reference count to determine when
> * to free an allocation if you use %__GFP_COMP (in which case, you may
> * as well use put_page() to free the page). Another thread may have a
> * speculative reference to the first page, but it has no way of knowing
> * about the rest of the allocation, so we have to free all but the
> * first page here.
> *
> * Context: May be called in interrupt context but not NMI context.
> */
>
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2020-09-29 7:26 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 [this message]
2020-09-29 14:06 ` Matthew Wilcox
2020-09-30 9:17 ` Mike Rapoport
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200929072622.GN2645148@linux.ibm.com \
--to=rppt@linux.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=hch@lst.de \
--cc=hughd@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=npiggin@gmail.com \
--cc=peterz@infradead.org \
--cc=rdunlap@infradead.org \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).