Messages in this thread | | | Date | Thu, 25 Jun 2009 16:37:43 -0400 | From | Theodore Tso <> | Subject | Re: upcoming kerneloops.org item: get_page_from_freelist |
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On Thu, Jun 25, 2009 at 01:18:59PM -0700, David Rientjes wrote: > Isn't there also a problem in jbd2_journal_write_metadata_buffer(), > though? > > tmp = jbd2_alloc(bh_in->b_size, GFP_NOFS); ... > memcpy(tmp, mapped_data + new_offset, jh2bh(jh_in)->b_size); > > jbd2_alloc() is just a wrapper to __get_free_pages() and if it fails, it > appears as though the memcpy() would cause a NULL pointer.
Nicely spotted. Yeah, that's a bug; we need to do something about that one, too. And what we're doing is a bit silly; it may make sense to use __get_free_pages if filesystem blocksize == PAGE_SIZE, but otherwise we should be using a sub-page allocator. Right now, we're chewing up a 16k PPC page for every 4k filesystem metadata page allocated in journal_write_metadata_buffer(), and on x86, for the (admittedly uncommon) 1k block filesystem, we'd be chewing up a 4k page for a 1k block buffer.
Both of these problems exist for both ext3 and ext4.
- Ted
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