From: "Chen Lin" <chen45464546@163.com>
To: "Alexander Duyck" <alexander.duyck@gmail.com>
Cc: "Maurizio Lombardi" <mlombard@redhat.com>,
"Jakub Kicinski" <kuba@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>
Subject: Re:Re: Re: [PATCH V3] mm: prevent page_frag_alloc() from corrupting the memory
Date: Wed, 20 Jul 2022 06:27:00 +0800 (CST) [thread overview]
Message-ID: <8a7e9cf.1b9.18218925734.Coremail.chen45464546@163.com> (raw)
In-Reply-To: <CAKgT0Uejy66aFAdD+vMPYFtSu2BWRgTxBG0mO+BLayk3nNuQMw@mail.gmail.com>
At 2022-07-18 23:33:42, "Alexander Duyck" <alexander.duyck@gmail.com> wrote:
>On Mon, Jul 18, 2022 at 8:25 AM Maurizio Lombardi <mlombard@redhat.com> wrote:
>>
>> po 18. 7. 2022 v 16:40 odesílatel Chen Lin <chen45464546@163.com> napsal:
>> >
>> > But the original intention of page frag interface is indeed to allocate memory
>> > less than one page. It's not a good idea to complicate the definition of
>> > "page fragment".
>>
>> I see your point, I just don't think it makes much sense to break
>> drivers here and there
>> when a practically identical 2-lines patch can fix the memory corruption bug
>> without changing a single line of code in the drivers.
>>
>> By the way, I will wait for the maintainers to decide on the matter.
>>
>> Maurizio
>
>I'm good with this smaller approach. If it fails only under memory
>pressure I am good with that. The issue with the stricter checking is
>that it will add additional overhead that doesn't add much value to
>the code.
>
>Thanks,
>
>- Alex
One additional question:
I don't understand too much about why point >A< have more overhead than point >B<.
It all looks the same, except for jumping to the refill process, and the refill is a very long process.
Could you please give more explain?
if (unlikely(offset < 0)) {
-------------->A<------------
page = virt_to_page(nc->va);
if (!page_ref_sub_and_test(page, nc->pagecnt_bias))
goto refill;
if (unlikely(nc->pfmemalloc)) {
free_the_page(page, compound_order(page));
goto refill;
}
#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
/* if size can vary use size else just use PAGE_SIZE */
size = nc->size;
#endif
/* OK, page count is 0, we can safely set it */
set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1);
/* reset page count bias and offset to start of new frag */
nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
offset = size - fragsz;
-------------->B<------------
}
next prev parent reply other threads:[~2022-07-19 22:28 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-15 12:50 [PATCH V3] mm: prevent page_frag_alloc() from corrupting the memory Maurizio Lombardi
2022-07-18 13:14 ` Chen Lin
2022-07-18 13:50 ` [PATCH " Maurizio Lombardi
2022-07-18 14:40 ` Chen Lin
2022-07-18 15:25 ` Maurizio Lombardi
2022-07-18 15:33 ` Alexander Duyck
2022-07-19 22:27 ` Chen Lin [this message]
2022-07-20 14:54 ` Alexander Duyck
2022-07-21 13:05 ` Chen Lin
[not found] ` <62aacb46.a9b1.182110646cf.Coremail.chen45464546@163.com>
2022-07-18 13:46 ` Maurizio Lombardi
2022-08-09 0:14 ` Andrew Morton
2022-08-09 11:45 ` Maurizio Lombardi
2022-08-09 14:33 ` Alexander Duyck
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