Messages in this thread | | | Date | Mon, 9 Oct 2006 13:40:41 +0200 | From | Jan Kara <> | Subject | Re: [PATCH 0/3] Fix IO error reporting on fsync() |
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> On Fri, 6 Oct 2006 13:49:47 +0200 > Jan Kara <jack@suse.cz> wrote: > > > current code in buffer.c has two pitfalls that cause problems with IO > > error reporting of filesystems using mapping->private_list for their > > metadata buffers (e.g. ext2). > > The first problem is that end_io_async_write() does not mark IO error > > in the buffer flags, only in the page flags. Hence fsync_buffers_list() > > does not find out that some IO error has occured and will not report it. > > The second problem is that buffers from private_list can be freed > > (e.g. under memory pressure) and if fsync_buffer_list() is called after > > that moment, IO error is lost - note that metadata buffers mark AS_EIO > > on the *device mapping* not on the inode mapping. > > Following series of three patches tries to fix these problems. The > > approach I took (after some discussions with Andrew) is introducing > > dummy buffer_head in the mapping instead of private_list. This dummy > > buffer head serves as a head of metadata buffer list and also collects > > IO errors from other buffers on the list (see the third patch for more > > details). This is kind of compromise between introducing a pointer to > > inode's address_space into each buffer and between using list_head > > instead of buffer_head and playing some dirty tricks to recognize that > > one particular list_head is actually from address_space and not from > > buffer_head. Any suggestions for improvements welcome. > > This is really complex, and enlarges the inode by quite a lot, which hurts. I agree (at least with the second part ;). I can write a patch which keeps the inode size but the code will be uglier... Another possibility is to put there just a buffer_head pointer and allocate buffer head dynamically. That has an advantage that only filesystems using metadata_list has to bear the memory cost...
> What about putting an address_space* into the buffer_head? Transfer the > EIO state into the address_space within, say, __remove_assoc_queue()? Yes, that's of course possible. But it enlarges each buffer head by 4 bytes (or 8 on 64-bit arch). Hmm, but you are right that on the systems I've looked at this would actually be less memory. OK, I'll write this version of the patch. Honza -- Jan Kara <jack@suse.cz> SuSE CR Labs - 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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