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Re: removing an ext2fs file forces disk activity
From: |
Thomas Bushnell, BSG |
Subject: |
Re: removing an ext2fs file forces disk activity |
Date: |
25 Mar 2002 13:36:20 -0800 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.1 |
nisse@lysator.liu.se (Niels Möller) writes:
> How hard would it be to create a new store type that basically
> implements only a write-cache: It would have store_write put the
> modified block into a queue, from which blocks are written to the
> underlying store later by a separate syncing thread. store_read would
> have to check this queue for blocks that are modified but not yet
> written to disk, but would otherwise just pass the read on to the
> underlying store.
This is fine, but here's the problem:
If the following sequence of writes comes from the filesystem:
write block A
write block B
write block A
you *cannot* in general omit the first write and coalesce them into a
single write.
Sometimes you can coalesce them, but it depends on exactly what is
happening in the filesystem.
This problem cannot be solved in the store; it has to be taken care of
by the filesystem.
> I'm a little confused about the interface between the filesystem and
> its store, I remember the talk about filesystems using mmap, but when
> I grep through the source for ext2fs and libdiskfs, I find some uses
> of store_read and store_write in ext2fs/pager.c, and no references at
> all to store_map. Actually, greping the entire hurd source for
> store_map, I can find only one single function that sues it:
> storeio/pager.c:dev_get_memory_object.
Filesystems have their own pager, because they need more control over
what happens than is provided by the store maps.
- Re: removing an ext2fs file forces disk activity, (continued)
Re: removing an ext2fs file forces disk activity, Jon Arney, 2002/03/25
- Re: removing an ext2fs file forces disk activity, Niels Möller, 2002/03/25
- Re: removing an ext2fs file forces disk activity, Marcus Brinkmann, 2002/03/25
- Re: removing an ext2fs file forces disk activity, Niels Möller, 2002/03/25
- Re: removing an ext2fs file forces disk activity, Marcus Brinkmann, 2002/03/25
- Re: removing an ext2fs file forces disk activity, Thomas Bushnell, BSG, 2002/03/25
- Re: removing an ext2fs file forces disk activity, Niels Möller, 2002/03/26
- Re: removing an ext2fs file forces disk activity, Thomas Bushnell, BSG, 2002/03/26
Re: removing an ext2fs file forces disk activity,
Thomas Bushnell, BSG <=
Re: removing an ext2fs file forces disk activity, Marcus Brinkmann, 2002/03/25
Re: removing an ext2fs file forces disk activity, Jon Arney, 2002/03/27