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    SubjectRe: Page cache and swapping

    1. to the one saying qsort'ing mmaped file would be agood idea:

    if you qsort a file that does not fit in memory, your program
    is nearly broken - qsort has almost no locality, so you
    get what you deserve... slow performance. qsort is one
    of the worst sorting algorithms for this case.

    >> 1. If page->count = 1 and the page is in page cache, it belongs exactly
    >> to one process. Right? Why is it simply freed by shrink_mmap and why
    >> it can't be freed, if page->count > 1?. Where is it removed from the process
    >> page table? Or rather the "present" bit is set to zero for page cache
    >> pages.
    >This is the difficult point - you need to walk the page tables of all
    >processes to find out which ones are using the page - a very costly
    >operation. This is why the current system doesn't do this.

    One point: when linux has started swapping, you have 50-95% IDLE time,
    because almost NO process can run. In this (quite normal scenario), you
    *do* have quite enough time to do almost any operation you want.

    Imagine the time it needs to write a single page to swap.. in that time
    you can do many thousands of memory accesses - and would still
    be faster when only saving ONE page form swapping.


    for a pentium-optimizing gcc, look at

    ----==-- _
    ---==---(_)__ __ ____ __ Marc Lehmann
    --==---/ / _ \/ // /\ \/ /
    -=====/_/_//_/\_,_/ /_/\_\
    The choice of a GNU generation

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