Date: Fri, 10 Jul 2020 10:37:32 +0200 From: Mateusz Guzik <mjguzik@gmail.com> To: "Piotr P. Stefaniak" <pstef@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r363068 - head/sys/kern Message-ID: <CAGudoHGE7a9VqDe4RbLCoADp4h42CXe0e1s8F6=ANtdMCmVJRQ@mail.gmail.com> In-Reply-To: <CAGudoHFCsJ4PUuM0Xixdf9haCObWz8wdDzx48BEoqJ7=%2B5u7QA@mail.gmail.com> References: <202007100646.06A6kgnX015296@repo.freebsd.org> <20200710082549.GC74062@freefall.freebsd.org> <CAGudoHFCsJ4PUuM0Xixdf9haCObWz8wdDzx48BEoqJ7=%2B5u7QA@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 7/10/20, Mateusz Guzik <mjguzik@gmail.com> wrote:
> On 7/10/20, Piotr P. Stefaniak <pstef@freebsd.org> wrote:
>>> */
>>>- memcpy(sbp, &mp->mnt_stat, sizeof(*sbp));
>>>+ if (sbp != &mp->mnt_stat)
>>>+ memcpy(sbp, &mp->mnt_stat, sizeof(*sbp));
>>>
>>
>> Slightly unrelated question: wouldn't it be prudent to incorporate this
>> logic into memcpy?
>>
>
> Calls like that are just abusing the routine and indicate design
> problems in the consumer.
> Adding the branch into the routine would add overhead for everyone.
>
> However, now that you mention it, it may be prudent to do something like
> this:
>
> dtrace -n 'fbt::memcpy:entry,fbt::memmove:entry /arg1 == arg2/ {
> @[stack()] = count(); }'
>
> and run your favourite workload.
>
Oops, that should be:
dtrace -n 'fbt::memcpy:entry,fbt::memmove:entry /arg0 == arg1/ {
@[stack()] = count(); }'
You can look for other abuse too, here are 0-sized calls:
dtrace -n 'fbt::memcpy:entry,fbt::memmove:entry,fbt::memset:entry
/arg2 == 0/ { @[probefunc,stack()] = count(); }'
--
Mateusz Guzik <mjguzik gmail.com>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAGudoHGE7a9VqDe4RbLCoADp4h42CXe0e1s8F6=ANtdMCmVJRQ>