[systemd-devel] [PATCH] [RFC][PLEASE TEST] readahead: chunk on spinning media

Andrey Borzenkov arvidjaar at gmail.com
Sat Mar 23 20:53:23 PDT 2013

В Sat, 23 Mar 2013 23:47:52 +0100
Lennart Poettering <lennart at poettering.net> пишет:

> On Sat, 23.03.13 23:42, Tom Gundersen (teg at jklm.no) wrote:
> > 
> > On Sat, Mar 23, 2013 at 2:16 AM, Lennart Poettering
> > <lennart at poettering.net> wrote:
> > > Then, I generally believe better than trying to be smart when reading
> > > things we should much rather try to place things properly on disk. We
> > > already defrag things based on the read order for btrfs, we should do
> > > the same for ext4. The API for that unfortunately awful, but e4rat has
> > > shown that this does work. Basically, this is what you do:
> > 
> > Isn't the problem that reads by blkid and friends are not being caught
> > by readahead-collect, and hence end up blocking until readahead-replay
> > has finished? In that case reordering won't help (I think).
> Hmm, if root file system is mounted the file system's superblock should
> be cached in memory, I'd expect, so blkid shouldn't have to block...

Filesystem caches superblock copy, not physical device block(s) where
it is located. After it is copied, blocks are not more in use.

More information about the systemd-devel mailing list