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vfs, ubc and pre-fetching on snow leopard
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vfs, ubc and pre-fetching on snow leopard

I reboot and run Firefox using the same arguments but get completely different page-in patterns every time. Why does this happen and how does this work?

How does the VFS determine the pages to fetch and the number of pages?

I'm trying to optimize disk access during cold startup of Firefox and I thought I'd reorder the symbols in the dylib by time. I determined that the function call chain during startup is A, B, C, D, E, F. I assumed that by ordering the symbols this way I'll get sequential disk access which doesn't seem to be the case.

I monitor page-ins using a simple dtrace script [1]. I then translate these page-ins to actual segments and sections of the XUL dynamic library using the output from 'size -m -l XUL'.

One run may give me (head -10 ...)

__LINKEDIT, __symtab = 2 pages, 5016 pages in
__LINKEDIT, __symtab = 2 pages, 5018 pages in
__DATA, __const = 4 pages, 4850 pages in
__DATA, __const = 4 pages, 4854 pages in
__DATA, __const = 4 pages, 4858 pages in
__DATA, __const = 4 pages, 4862 pages in
__DATA, __const = 4 pages, 4866 pages in

whereas another run

__LINKEDIT, __symtab = 2 pages, 5016 pages in
__DATA, __const = 5 pages, 4921 pages in
__DATA, __const = 6 pages, 4956 pages in
__DATA, __data = 7 pages, 4998 pages in
__TEXT, __const = 40 pages, 256 pages in
__TEXT, __cstring = 44 pages, 307 pages in
__TEXT, __text = 73 pages, 2390 pages in

Where in the kernel is the logic that's applied here and what's the proper way to optimize my disk access?

	Thanks, Joel

[1] xul-pageins.d

  self->v_name = stringof(((vnode_t)arg0)->v_name);

/self->v_name == "XUL"/
  printf("vnode_pagein: %s, offset: %u, size: %u\n",
    self->v_name, arg3, arg4);

firefox for android!

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