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From: Kent Overstreet To: David Wang <00107082@163.com> Cc: Suren Baghdasaryan , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] alloc_tag: avoid mem alloc and iter reset when reading allocinfo Message-ID: References: <20250507175500.204569-1-00107082@163.com> <289b58f1.352d.196addbf31d.Coremail.00107082@163.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <289b58f1.352d.196addbf31d.Coremail.00107082@163.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 81BB91C0004 X-Stat-Signature: xz1xnnnknr6mwfd1ywqcy5s7sdrj1hfd X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1746675079-595289 X-HE-Meta: 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 C6AHXch9 KQJrWwNDmpgEwd2aBY2OfYa0Jq1ccNzmHrRS1fVUz7oJPkwQGnKnbx8OHIq/WEcv8jwLDXbzgG/pYIPu+vzXD8Ab+nWwpxAmimMKFsrB7EgGfL6ZlRooRe7JEKFXUD/M8VhzQ6KSmXj3Q4c/Gd1YvNLE4dCOc7PpyL7WTEQoJpgmipCjTft/yu23JB2cIB6z/hD+W+ALIdWgQCaX++FKtJKu/Q3+bYPGvaxwb 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: List-Subscribe: List-Unsubscribe: On Thu, May 08, 2025 at 11:06:35AM +0800, David Wang wrote: > Thanks for the feedback~ > I agree that memory allocation normally dose not take major part of a profiling report, > even profiling a fio test, kmem_cache_alloc only takes ~1% perf samples. > > I don't know why I have this "the less memory allocation, the better' mindset, maybe > I was worrying about memory fragmentation, or something else I learned on some "textbook", > To be honest, I have never had real experience with those worries.... It's a common bias. "Memory allocations" take up a lot of conceptual space in our heads, and generally for good reason - i.e. handling memory allocation errors is often a major concern, and you do always want to be aware of memory layout. But this can turn into an aversion that's entirely disproportionate - e.g. using linked linked lists and fixed size arrays in ways that are entirely inappropriate, instead of vectors and other better data structures; good data structures always require allocations. Profile, profile, profile, and remember your basic CS (big O notation) - 90% of the time, simple code with good big O running time is all you need.