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

[Andrey Borzenkov]

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.