linux-kernel - Re: [PATCH v2 0/7] Add io_dir to avoid memory overhead from opendir

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Message-ID: <20250208105821.1cdb54fc@pumpkin>
Date: Sat, 8 Feb 2025 10:58:21 +0000
From: David Laight <david.laight.linux@...il.com>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim
 <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, Alexander
 Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa
 <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, Kan Liang
 <kan.liang@...ux.intel.com>, Sam James <sam@...too.org>, Jesper Juhl
 <jesperjuhl76@...il.com>, James Clark <james.clark@...aro.org>, Zhongqiu
 Han <quic_zhonhan@...cinc.com>, Yicong Yang <yangyicong@...ilicon.com>,
 Thomas Richter <tmricht@...ux.ibm.com>, Michael Petlan
 <mpetlan@...hat.com>, Veronika Molnarova <vmolnaro@...hat.com>, Anne Macedo
 <retpolanne@...teo.net>, Dominique Martinet <asmadeus@...ewreck.org>,
 Jean-Philippe Romain <jean-philippe.romain@...s.st.com>, Junhao He
 <hejunhao3@...wei.com>, linux-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org, "Krzysztof Łopatowski"
 <krzysztof.m.lopatowski@...il.com>
Subject: Re: [PATCH v2 0/7] Add io_dir to avoid memory overhead from opendir

On Fri,  7 Feb 2025 15:24:41 -0800
Ian Rogers <irogers@...gle.com> wrote:

> glibc's opendir allocates a minimum of 32kb, when called recursively
> for a directory tree the memory consumption can add up - nearly 300kb
> during perf start-up when processing modules. Add a stack allocated
> variant of readdir sized a little more than 1kb

Does 300kB really matter?

You seem to be trading memory allocation against system calls.
My 'gut feel' is that the system call cost will dominate.
(Unless all the directories are small.)

There might, of course, be other code in glibc that is designed
to make it all slower than necessary.

	David