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Re: Review of Thomas's >2GB ext2fs proposal

From: Ognyan Kulev
Subject: Re: Review of Thomas's >2GB ext2fs proposal
Date: Tue, 17 Aug 2004 12:29:46 +0300
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040413 Debian/1.6-5

Thomas Bushnell BSG wrote:
I only cache mappings, so it doesn't really matter.  Creating mappings
is very very cheap (especially if you allow Mach to pick the addresses
by using the anywhere flag).  Creating mappings is just vm_map, which
is speedy and quick--it's the same as vm_allocate.  But I would use
LRU for lack of something else.

Mappings carry no overhead, and are quick and easy to set up and tear

This is new to me.  I always thought that vm_map/vm_unmap is expensive.

Currently, the ext2fs patch uses fixed-size cache of pages, which are used to map and unmap different disk blocks. But it will be much more flexible if we have set of vm_mapped pages. Requesting unmapped disk block vm_maps page (where Mach decides) that contains that block. Evicting this page automatically (by ext2fs) vm_unmaps it too. All these pages are part of the same pager that grows as necessary.


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