From: Al Viro <viro@zeniv.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Michael Kerrisk <mtk.manpages@gmail.com>,
shuah@kernel.org, Linux API <linux-api@vger.kernel.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-man <linux-man@vger.kernel.org>,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 1/3] readfile: implement readfile syscall
Date: Sat, 4 Jul 2020 21:16:36 +0100 [thread overview]
Message-ID: <20200704201636.GE2786714@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200704201206.GD2786714@ZenIV.linux.org.uk>
On Sat, Jul 04, 2020 at 09:12:06PM +0100, Al Viro wrote:
> On Sat, Jul 04, 2020 at 09:41:09PM +0200, Miklos Szeredi wrote:
> > And "If the size of file is smaller than the value provided in count
> > then the whole file will be copied into buf", which is simply a lie;
> > for example seq_file will happily return a smaller-than-PAGE_SIZE
> > chunk if at least one record fits in there. You'll have a very hard
> > time explaining that in the man page. So I think there are two
> > possible ways forward:
> >
> > 1) just leave the first explanation (it's an open + read + close
> > equivalent) and leave out the rest
> >
> > 2) add a loop around the vfs_read() in the code.
>
> 3) don't bother with the entire thing, until somebody manages to demonstrate
> a setup where it does make a real difference (compared to than the obvious
> sequence of syscalls, that is). At which point we'll need to figure out
> what's going on and deal with the underlying problem of that setup.
Incidentally, if that's intended for use on _sysfs_, I would like to see the
effects of that sucker being called by many processes in parallel, seeing that
sysfs has, er, certain scalability problems in its lookups. And I would be
very surprised if they were not heavier than said overhead of two extra syscalls.
next prev parent reply other threads:[~2020-07-04 20:16 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-04 14:02 [PATCH 0/3] readfile(2): a new syscall to make open/read/close faster Greg Kroah-Hartman
2020-07-04 14:02 ` [PATCH 1/3] readfile: implement readfile syscall Greg Kroah-Hartman
2020-07-04 18:35 ` Geert Uytterhoeven
2020-07-04 19:14 ` Matthew Wilcox
2020-07-04 19:41 ` Miklos Szeredi
2020-07-04 20:12 ` Al Viro
2020-07-04 20:16 ` Al Viro [this message]
2020-07-04 14:02 ` [PATCH 2/3] arch: wire up the " Greg Kroah-Hartman
2020-07-04 18:36 ` Geert Uytterhoeven
2020-07-04 14:02 ` [PATCH 3/3] selftests: add readfile(2) selftests Greg Kroah-Hartman
2020-07-04 18:38 ` Geert Uytterhoeven
2020-07-05 6:55 ` Greg Kroah-Hartman
2020-07-05 11:24 ` Geert Uytterhoeven
2020-07-05 11:36 ` Greg Kroah-Hartman
2020-07-05 1:41 ` Heinrich Schuchardt
2020-07-05 7:34 ` Greg Kroah-Hartman
2020-07-05 9:46 ` Heinrich Schuchardt
2020-07-04 14:02 ` [PATCH] readfile.2: new page describing readfile(2) Greg Kroah-Hartman
2020-07-05 2:54 ` Heinrich Schuchardt
2020-07-04 19:30 ` [PATCH 0/3] readfile(2): a new syscall to make open/read/close faster Al Viro
2020-07-05 11:47 ` Greg Kroah-Hartman
2020-07-06 17:25 ` Dave Martin
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