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SubjectRe: Avoiding OOM on overcommit...?
On Fri, 24 Mar 2000, Alexander Viro wrote:
>On Fri, 24 Mar 2000, David Whysong wrote:
>> On Fri, 24 Mar 2000, Alexander Viro wrote:
>> >RTFComments. Sharing of text pages is unrelated to overcommit.
>>
>> But demand loading certainly is related to overcommit, unless the kernel
>> was careful to count how many pages it hasn't loaded yet?
>
>There are _text_ pages. As in "ones that can be thrown away at any
>moment". Check what part of the binaries is mapped with write allowed.
>That's where demand loading may have something with overcommit.

And there are also data pages. From 1.0, fs/exec.c:

error = do_mmap(file, N_TXTADDR(ex) + ex.a_text, ex.a_data,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_FIXED | MAP_PRIVATE, N_TXTOFF(ex) +
ex.a_text);

do_mmap is also called for text, read-only.

The comments say:

* Demand-loading implemented 01.12.91 - no need to read anything but
* the header into memory. The inode of the executable is put into
* "current->executable", and page faults do the actual loading. Clean.

and later

* Demand loading changed July 1993 by Eric Youngdale. Use mmap instead,
* current->executable is only used by the procfs.

Looks to me like data was demand loaded in early kernels... and we're
completely ignoring stack growth, of course.

Dave

David Whysong dwhysong@physics.ucsb.edu
Astrophysics graduate student University of California, Santa Barbara
My public PGP keys are on my web page - http://www.physics.ucsb.edu/~dwhysong
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D-H PGP key 0x5DAB0F91 : BC33 0F36 FCCD E72C 441F 663A 72ED 7FB7 5DAB 0F91






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