Messages in this thread | | | Date | Sat, 30 Dec 2000 11:31:32 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: 2.2.19pre3 and poor reponse to RT-scheduled processes? |
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On Sat, 30 Dec 2000, Alexander Viro wrote: > On 30 Dec 2000, Linus Torvalds wrote: > > > There are other, equally likely, candidates for these kinds of stalls: > > > > - filesystem locks. Especially the ext2 superblock lock. You can easily > > hit this one, as some ext2 functions actually do a lot of IO while > > holding the lock. > > Hmm... In 2.4 we can make the situation with superblock lock on ext2 > much better.
Actually, 2.4.x right now is worse than 2.2.x in this regard, for a really simple reason: 2.2.x will only do the equivalent of "rebalance_dirty" when it dirties a previously clean buffer. The current 2.4.x code does that regardless of whether the buffer was dirty before or not.
I want to see your patches to fix this for good in a 2.5.x timeframe (or, if they are really clean and obvious, at a later 2.4.x date), but for 2.4.x I think that we'll do either "remove rebalance dirty completely" or at the very least we'll not re-balance for re-dirtying a dirty buffer.
The re-dirtying a dirty buffer is the common case for the superblock stuff: bitmap blocks etc are often dirty already, _especially_ in the case of an active writer. So 2.4.x is actually more likely to hit the superblock/bdflush contention.
Of course, 2.4.x has had so many improvements in file writing memory pressure that it might not end up being that noticeable, but even so..
Linus
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