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Date: Fri, 16 Aug 2002 03:57:17 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: Benjamin LaHaise <bcrl@redhat.com>
Cc: Linus Torvalds <torvalds@transmeta.com>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Chris Friesen <cfriesen@nortelnetworks.com>,
       Pavel Machek <pavel@elf.ucw.cz>, linux-kernel@vger.kernel.org,
       linux-aio@kvack.org
Subject: Re: aio-core why not using SuS? [Re: [rfc] aio-core for 2.5.29 (Re: async-io API registration for 2.5.29)]
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On Thu, Aug 15, 2002 at 09:42:25PM -0400, Benjamin LaHaise wrote:
> Read it again.  You've totally missed lio_listio.  Also keep in mind what 

you're saying you prefer glibc to wrap the aio_read/write/fsync and to
redirect all them to lio_listio after converting the iocb from user API to
kernel API, right? still I don't see why should we have different iocb,
I would understsand if you say we should simply overwrite aio_lio_opcode
inside the aio_read(3) inside glibc and to pass it over to kernel with a
single syscalls if it's low cost to just set the lio_opcode, but having
different data structures doesn't sounds the best still. I mean, it
would be nicer if things would be more consistent.

> happens with 4G/4G split for x86 which are needed to address the kernel 
> virtual memory starvation issues.

I don't see how the flushing flood is related to this, this is a normal
syscall, any issue that applies to these aio_read/write/fsync should
apply to all other syscalls too. Also the 4G starvation will be more
likely fixed by x86-64 or in software by using a softpagesize larger
than 4k so that the mem_map array doesn't load all the zone_normal.
That'll break backwards compatibility w.r.t. to the page size offset but
it'll at least not generate a so significant performance regression for
syscall performance (again this is generic issue, not related to
async-io as far as I can tell).

Andrea
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