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Thu, 15 Aug 2024 12:18:19 -0700 (PDT) MIME-Version: 1.0 References: <20240813042917.506057-1-andrii@kernel.org> <20240813042917.506057-14-andrii@kernel.org> <7byqni7pmnufzjj73eqee2hvpk47tzgwot32gez3lb2u5lucs2@5m7dvjrvtmv2> In-Reply-To: From: Arnaldo Carvalho de Melo Date: Thu, 15 Aug 2024 16:18:07 -0300 Message-ID: Subject: Re: [PATCH RFC v3 13/13] uprobes: add speculative lockless VMA to inode resolution To: Mateusz Guzik Cc: Jann Horn , Suren Baghdasaryan , Christian Brauner , Andrii Nakryiko , Andrii Nakryiko , linux-trace-kernel@vger.kernel.org, peterz@infradead.org, oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, akpm@linux-foundation.org, linux-mm@kvack.org Content-Type: multipart/alternative; boundary="0000000000009ed11a061fbdb499" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D8DFA4000E X-Stat-Signature: 77cpcbjng94x35bagz1imfmanp487zae X-HE-Tag: 1723749500-731936 X-HE-Meta: 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 BnNHY6lt a9R74sLkb6guUK+oM9yN5HQFSE4Z5NoKLf26Fh7A+OD4z/md5AxZHdYiZiF5++iJgCT7TV18Tq2JviZy+B3UncMEkGua2pa/CvA6aPwGp0rdryFhj3Y7zSNxzC5lb1JJ+T+VyBL2O8jwBNOus4fKvG4gJvVtcd7g/M5iHM3PeKeCM/A05awBWlgs8hzAH/zqfL+SnhUfgOsbtp5v7M5d0dnGdCHHpTwxkHbGHR9fiS4sL6VTR7y4WHCdj45qPOjT6NKFMxy/mUSKYvthPoo29m8EaeAyuijESxwFtp9ct7fvaI4zMe1RKTjp3DKWbpgl5VBSIYvlCtHCfC3Wm97WkLoh6dd+X0TGZ72V09/HOL/0W7EXzGyR6x1pyXpo2Rxm6Rig3jJ/qaZG75v2L+7dGrs1nzdtFm9wFGVb7E/kFdT6wG8AV7I5WbMkyxrt6om/RJIcqdvtKeV6AM2rqKo2kS293bzuRt22dQKrfJ6/eu17PeI9Tgrx8ho1zXX6JcaVtrC4jf8HvrDSsLlDGBJTr6Pwxc3Bt1QGR2nRLkGuIb+HMQIc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.185564, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --0000000000009ed11a061fbdb499 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sorry, nevermind, wrong forward :-/ On Thu, Aug 15, 2024, 4:17=E2=80=AFPM Arnaldo Carvalho de Melo < arnaldo.melo@gmail.com> wrote: > Um exemplo de uma modifica=C3=A7=C3=A3o numa =C3=A1rea central derivada d= e uma > necessidade espec=C3=ADfica: melhorar a performance de uprobes > > On Thu, Aug 15, 2024, 4:07=E2=80=AFPM Mateusz Guzik w= rote: > >> On Thu, Aug 15, 2024 at 8:58=E2=80=AFPM Jann Horn wro= te: >> > Stupid question: Is this uprobe stuff actually such a hot codepath >> > that it makes sense to optimize it to be faster than the page fault >> > path? >> > >> >> That's what I implicitly asked, hoping a down_read on vma would do it, >> but Andrii claims multiple parallel lookups on the same vma are a >> problem. >> >> Even so, I suspect something *simple* is doable here which avoids any >> writes to vmas and does not need the mm-wide sequence counter. It may >> be requirements are lax enough that merely observing some state is the >> same before and after uprobe lookup will be sufficient, or maybe some >> other hackery is viable without messing with fences in >> vma_start_write. >> -- >> Mateusz Guzik >> >> --0000000000009ed11a061fbdb499 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

Sorry, nevermind, wrong forward :-/


On Thu= , Aug 15, 2024, 4:17=E2=80=AFPM Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com> wrote:
=

Um exemplo de uma modifica=C3= =A7=C3=A3o numa =C3=A1rea central derivada de uma necessidade espec=C3=ADfi= ca: melhorar a performance de uprobes


On Thu= , Aug 15, 2024, 4:07=E2=80=AFPM Mateusz Guzik <mjguzik@gmail.com> = wrote:
On Thu, Aug 15, 2024 at 8:58= =E2=80=AFPM Jann Horn <jannh@google.com> wrote:
> Stupid question: Is this uprobe stuff actually such a hot codepath
> that it makes sense to optimize it to be faster than the page fault > path?
>

That's what I implicitly asked, hoping a down_read on vma would do it,<= br> but Andrii claims multiple parallel lookups on the same vma are a
problem.

Even so, I suspect something *simple* is doable here which avoids any
writes to vmas and does not need the mm-wide sequence counter. It may
be requirements are lax enough that merely observing some state is the
same before and after uprobe lookup will be sufficient, or maybe some
other hackery is viable without messing with fences in
vma_start_write.
--
Mateusz Guzik <mjguzik gmail.com>

--0000000000009ed11a061fbdb499--