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From: Kent Overstreet To: Tejun Heo Cc: Michal Hocko , Suren Baghdasaryan , akpm@linux-foundation.org, vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, corbet@lwn.net, void@manifault.com, peterz@infradead.org, juri.lelli@redhat.com, ldufour@linux.ibm.com, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, dennis@kernel.org, muchun.song@linux.dev, rppt@kernel.org, paulmck@kernel.org, pasha.tatashin@soleen.com, yosryahmed@google.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, andreyknvl@gmail.com, keescook@chromium.org, ndesaulniers@google.com, gregkh@linuxfoundation.org, ebiggers@google.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, shakeelb@google.com, songmuchun@bytedance.com, jbaron@akamai.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, kasan-dev@googlegroups.com, cgroups@vger.kernel.org Subject: Re: [PATCH 00/40] Memory allocation profiling Message-ID: References: <20230501165450.15352-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 03, 2023 at 06:35:49AM -1000, Tejun Heo wrote: > Hello, Kent. > > On Wed, May 03, 2023 at 04:05:08AM -0400, Kent Overstreet wrote: > > No, we're still waiting on the tracing people to _demonstrate_, not > > claim, that this is at all possible in a comparable way with tracing. > > So, we (meta) happen to do stuff like this all the time in the fleet to hunt > down tricky persistent problems like memory leaks, ref leaks, what-have-you. > In recent kernels, with kprobe and BPF, our ability to debug these sorts of > problems has improved a great deal. Below, I'm attaching a bcc script I used > to hunt down, IIRC, a double vfree. It's not exactly for a leak but leaks > can follow the same pattern. > > There are of course some pros and cons to this approach: > > Pros: > > * The framework doesn't really have any runtime overhead, so we can have it > deployed in the entire fleet and debug wherever problem is. > > * It's fully flexible and programmable which enables non-trivial filtering > and summarizing to be done inside kernel w/ BPF as necessary, which is > pretty handy for tracking high frequency events. > > * BPF is pretty performant. Dedicated built-in kernel code can do better of > course but BPF's jit compiled code & its data structures are fast enough. > I don't remember any time this was a problem. You're still going to have the inherent overhead a separate index of outstanding memory allocations, so that frees can be decremented to the correct callsite. The BPF approach is going to be _way_ higher overhead if you try to use it as a general profiler, like this is.