Messages in this thread | | | Date | Tue, 10 Aug 2004 16:04:55 -0300 | From | Marcelo Tosatti <> | Subject | Re: [PATCH] reserved buffers only for PF_MEMALLOC |
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On Tue, Aug 10, 2004 at 01:20:24PM -0400, Rik van Riel wrote: > > The buffer allocation path in 2.4 has a long standing bug, > where non-PF_MEMALLOC tasks can dig into the reserved pool > in get_unused_buffer_head(). The following patch makes the > reserved pool only accessible to PF_MEMALLOC tasks. > > Other processes will loop in create_buffers() - the only > function that calls get_unused_buffer_head() - and will call > try_to_free_pages(GFP_NOIO), freeing any buffer heads that > have become freeable due to IO completion. > > Note that PF_MEMALLOC tasks will NOT do anything inside > try_to_free_pages(), so it is needed that they are able to > dig into the reserved buffer heads while other tasks are > not.
Sounds the correct thing to do, thanks.
Out of curiosity: Do you actually seen any practical problem due to get_unused_buffer_head() calls eating into the reserved pool?
Or have any testcase which would trigger a problem (OOM) due to it? > > Signed-off-by: Rik van Riel <riel@redhat.com> > > --- linux/fs/buffer.c.deadlock 2004-08-10 11:33:08.000000000 -0400 > +++ linux/fs/buffer.c 2004-08-10 11:34:54.000000000 -0400 > @@ -1260,8 +1260,9 @@ struct buffer_head * get_unused_buffer_h > > /* > * If we need an async buffer, use the reserved buffer heads. > + * Non-PF_MEMALLOC tasks can just loop in create_buffers(). > */ > - if (async) { > + if (async && (current->flags & PF_MEMALLOC)) { > spin_lock(&unused_list_lock); > if (unused_list) { > bh = unused_list; - 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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