Messages in this thread | | | Date | Thu, 25 Apr 2013 20:16:45 +0400 | From | "Maxim V. Patlasov" <> | Subject | Re: [fuse-devel] [PATCH 14/14] mm: Account for WRITEBACK_TEMP in balance_dirty_pages |
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Hi,
04/25/2013 07:49 PM, Miklos Szeredi пишет: > On Thu, Apr 25, 2013 at 4:29 PM, Maxim V. Patlasov > <mpatlasov@parallels.com> wrote: >>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c >>> index 0713bfb..c47bcd4 100644 >>> --- a/mm/page-writeback.c >>> +++ b/mm/page-writeback.c >>> @@ -1235,7 +1235,8 @@ static void balance_dirty_pages(struct address_space >>> *mapping, >>> */ >>> nr_reclaimable = global_page_state(NR_FILE_DIRTY) + >>> >>> global_page_state(NR_UNSTABLE_NFS); >>> - nr_dirty = nr_reclaimable + >>> global_page_state(NR_WRITEBACK); >>> + nr_dirty = nr_reclaimable + >>> global_page_state(NR_WRITEBACK) + >>> + global_page_state(NR_WRITEBACK_TEMP); >>> global_dirty_limits(&background_thresh, &dirty_thresh); >> >> Please drop this patch. As we discussed in LSF/MM, the fix above is correct, >> but it's not enough: we also need to ensure disregard of NR_WRITEBACK_TEMP >> when balance_dirty_pages() is called from fuse daemon. I'll send a separate >> patch-set soon. > Please elaborate. From a technical perspective "fuse daemon" is very > hard to define, so anything that relies on whether something came from > the fuse daemon or not is conceptually broken.
As Mel Gorman pointed out, fuse daemon diving into balance_dirty_pages should not kick flusher judging on NR_WRITEBACK_TEMP. Essentially, all we need in balance_dirty_pages is:
if (I'm not fuse daemon) nr_dirty += global_page_state(NR_WRITEBACK_TEMP);
The way how to identify fuse daemon was not thoroughly scrutinized during LSF/MM. Firstly, I thought it would be enough to set a per-process flag handling fuse device open. But now I understand that fuse daemon may be quite a complicated multi-threaded multi-process construction. I'm going to add new FUSE_NOTIFY to allow fuse daemon decide when it works on behalf of draining writeout-s. Having in mind that fuse-lib is multi-threaded, I'm also going to inherit the flag on copy_process(). Does it make sense for you?
Also, another patch will put this ad-hoc FUSE_NOTIFY under fusermount control. This will prevent malicious unprivileged fuse mounts from setting the flag for malicious purposes.
Thanks, Maxim -- 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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