linux-kernel - Re: Downsides to madvise/fadvise(willneed) for application startup

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Message-Id: <9BEF5F2C-8AF3-480A-B382-41B0D331DE7D@mit.edu>
Date:	Fri, 16 Apr 2010 08:23:17 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Andi Kleen <andi@...obates.de>
Cc:	Zan Lynx <zlynx@....org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Taras Glek <tglek@...illa.com>, linux-kernel@...r.kernel.org
Subject: Re: Downsides to madvise/fadvise(willneed) for application startup

On Apr 16, 2010, at 7:41 AM, Andi Kleen wrote:

> Zan Lynx <zlynx@....org> writes:
> 
>> On 4/15/10 4:53 PM, Andrew Morton wrote:
>> 
>>> This just isn't an interesting case.  World-wide, the number of people
>>> who compile their own web browser and execute it from the file which ld
>>> produced is, umm, seven.
>> 
>> Gentoo users? Linux From Scratch?
> 
> "make install" tends to copy. I am not aware of any Makefiles
> that link directly to /usr/bin, and usually that wouldn't work
> anyways because of permissions. copy fixes the problem.

... and those people who are executing the binary out of the build directory are probably running the regression  test (i.e., "make; make check") and on most developer machines, if they're lucky they have enough memory that the executable will still be in their page cache.   :-)

This being said, on modern file systems (i.e., btrfs, ext4, xfs, et. al), delayed allocation should mostly hide this problem; and if not, and the linker can estimate in advance how big the resulting binary will be, it could be modified to use the fallocate(2) system call.

-- Ted

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