Messages in this thread | | | Date | Sun, 9 Jan 2005 09:35:51 -0200 | From | Marcelo Tosatti <> | Subject | Re: [RFC] per thread page reservation patch |
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On Fri, Jan 07, 2005 at 03:43:05PM -0800, Andrew Morton wrote: > Nikita Danilov <nikita@clusterfs.com> wrote: > > > > > > > > Why does the filesystem risk going oom during the rebalance anyway? Is it > > > doing atomic allocations? > > > > No, just __alloc_pages(GFP_KERNEL, 0, ...) returns NULL. When this > > happens, the only thing balancing can do is to panic. > > __alloc_pages(GFP_KERNEL, ...) doesn't return NULL. It'll either succeed > or never return ;) That behaviour may change at any time of course, but it > does make me wonder why we're bothering with this at all. Maybe it's > because of the possibility of a GFP_IO failure under your feet or > something? > > What happens if reiser4 simply doesn't use this code? > > > If we introduce this mechanism, people will end up using it all over the > place. Probably we could remove radix_tree_preload(), which is the only > similar code I can I can immediately think of. > > Page reservation is not a bad thing per-se, but it does need serious > thought.
Whenever scheme comes up I dont think the current check in __alloc_pages() is any good:
if (order == 0) { page = perthread_pages_alloc(); if (page != NULL) return page; }
Two things:
- all instances of an allocator from the current thread will eat from the perthread reserves, you probably want only a few special allocations to eat from the reserves? Thing is its not really a reservation intended for emergency situations, rather a "generic per-thread pool" the way things are now.
- its a real fast path, we're adding quite some instructions there which are only used by reiserfs now.
I think in a "final" implementation emergency allocations should be explicitly stated as such by the callers ?
> How does reiser4 end up deciding how many pages to reserve? Gross > overkill? > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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