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"caching pager"

From: Ognyan Kulev
Subject: "caching pager"
Date: Fri, 15 Aug 2003 11:29:59 +0300
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030714 Debian/1.4-2


Thinking about ext2fs and ext3fs without 1G limit, an idea came to me. The purpose of this mail is that to be considered when redesigning libpager API and/or implementation.

The classic way in which filesystems work in monolithic kernels is using block cache. This block cache has no fixed size and spans free memory of system. Each block can be thrown away by the kernel at any given time if it is not locked.

Let's suppose our pager have 64-bit offsets (like in the Neal's patch an year and half ago). We can add two basic operations: map and throw_away. Mapping maps block/page/fragment at _random location_ in memory. Of course, it only seems random to user thread. The exact location is decided by the Hurd, glibc, and/or microkernel. When the Hurd, glibc, and/or microkernel decide that block is good candidate to be thrown away, throw_away is called. It is important that throw_away should be able to reject throwing away, for cases like block in use.

There are some details here, but this is the basic idea.

Ognyan Kulev <ogi@{fmi.uni-sofia.bg,fsa-bg.org}>
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