Re: uvm vm_physseg trimming

[Cherry G. Mathew <cherry%zyx.in@localhost>]

Hello after a long while.

>>>>> "Masao" == Masao Uebayashi <uebayasi%gmail.com@localhost> writes:

    Masao> avail_start/avail_end are used to keep track of the range
    Masao> used for "managed pages" - PAGE_SIZE'ed pages that are added
    Masao> to free list and allocated from there.  Managed pages are
    Masao> initially added after kernel reserves its internal, bootstrap
    Masao> memory region (.text, .data, ...).

    Masao> In some cases kernel wants to get ("steal") more memory, for
    Masao> its internal use, after it already gives all remaining memory
    Masao> pages to UVM.  See pmap_steal_memory().

    Masao> There are no clear design or requirement for MD code about
    Masao> how to use vm_physseg right now.  By merging `avail_start' to
    Masao> `start', you lose information of the original `start'; actual
    Masao> start physical address of a continuous physical memory
    Masao> segment.  And even without it, probably all ports will
    Masao> continue working, because nothing uses that information.

Right, so I began actually using it for its semantically relevant
purpose, and .....

    Masao> Personally I don't like that direction.  I wanted to make
    Masao> interfaces around vm_physseg and pmap/UVM bootstrap design
    Masao> clearer.  I wanted to keep more information into vm_physseg,
    Masao> instead of letting MD code invent their own paddr_t range
    Masao> management.

    Masao> I would suggest you to touch/massage those UVM/pmap/MD
    Masao> bootstrap code readily and carefully.  That is the only way
    Masao> to thoroughly understand such abandoned things.  Asking
    Masao> questions don't give you perfect answers.  Splitting
    Masao> vm_physseg handling from uvm_page.c into uvm_physseg.c would
    Masao> be a good start.

.... hid the vm_segment stuff behind a couple of files
(uvm_physmem.[ch]).

http://fooobar.mooo.com/~cherry/tmp/uvm_physmem2.diff

The result was surprisingly close to an API I have been working on for
hotplug, so this encourages me.

Stay tuned.....

-- 
~cherry