Re: Thread implementations...

[ebiederm+eric@npwt.net (Eric W. Biederman)]

>>>>> "ST" == Stephen C Tweedie <sct@dcs.ed.ac.uk> writes:

ST> Hi,
ST> On 24 Jun 1998 23:56:28 -0500, ebiederm+eric@npwt.net (Eric
ST> W. Biederman) said:

>> mmap, madvise(SEQUENTIAL),write 
>> is easy to implement.  The mmap layer already does readahead, all we
>> do is tell it not to be so conservative.

ST> Swap readhead is also now possible.  However, madvise(SEQUENTIAL) needs
ST> to do much more than this; 

In the long term I agree.  We can get a close approximation to the
proper behavior by simply doing aggressive readahead.  This is doable
now, and should work in the presence of multiple readers.

ST> it needs to aggressively track what region of
ST> the vma is being actively used, and to unmap those areas no longer in
ST> use.  (They can remain in cache until the memory is needed for something
ST> else, of course.)  The madvise is only going to be important if the
ST> whole file / vma does not fit into memory, 

Actally it will be important if the whole working set of data, (which
in a web server would be _all_ of it's files is too large to fit into
memory).  Each file /vma may fit in fine.

ST> so having advice that a piece
ST> of memory not recently accessed is unlikely to be accessed again until
ST> the next sequential pass is going to be very valuable.  It will prevent
ST> us from having to swap out more useful stuff.

Agreed.

Eric