Re: [PATCH] Re: Fwd: Re: memory usage - dentry_cacheg

Alexander Viro
2001-04-12T15:27:39Z

On Thu, 12 Apr 2001, Rik van Riel wrote:

> Please take a look at Ed Tomlinson's patch. It also puts pressure
> on the dcache and icache independent of VM pressure, but it does
> so based on the (lack of) pressure inside the dcache and icache
> themselves.
>
> The patch looks simple, sane and it might save us quite a bit of
> trouble in making the prune_{icache,dcache} functions both able
> to avoid low-memory deadlocks *AND* at the same time able to run
> fast under low-memory situations ... we'd just prune from the
> icache and dcache as soon as a "large portion" of the cache isn't
> in use.

Bad idea. If you do loops over directory contents you will almost
permanently have almost all dentries freeable. Doesn't make freeing
them a good thing - think of the effects it would have.

Simple question: how many of dentries in /usr/src/linux/include/linux
are busy at any given moment during the compile? At most 10, I suspect.
I.e. ~4%.

I would rather go for active keeping the amount of dirty inodes low,
so that freeing would be cheap. Doing massive write_inode when we
get low on memory is, indeed, a bad thing, but you don't have to
tie that to freeing stuff. Heck, IIRC you are using quite a similar
logics for pagecache...