A related question I had on writepages failures: what is the 'right' thing to do if we get a server error on writeback? If we believe it may be transient (say, ENOSPC), should we redirty pages and hope for better luck next time? What if we decide it's a fatal error? sage On Thu, 23 Jul 2009, Andi Kleen wrote: > Sage Weil <sage@xxxxxxxxxxxx> writes: > > > The ceph address space methods are concerned primarily with managing > > the dirty page accounting in the inode, which (among other things) > > must keep track of which snapshot context each page was dirtied in, > > and ensure that dirty data is written out to the OSDs in snapshort > > order. > > > > A writepage() on a page that is not currently writeable due to > > snapshot writeback ordering constraints is ignored (it was presumably > > called from kswapd). > > Not a detailed review. You would need to get one from someone who > knows the VFS interfaces very well (unfortunately those people are hard > to find). I just read through it. > > One thing I noticed is that you seem to do a lot of memory allocation > in the write out paths (some of it even GFP_KERNEL, not GFP_NOFS) > > The traditional wisdom is that you should not allocate memory in block > writeout, because that can deadlock. The worst case is swapfile > on it, but it can happen with mmap too (e.g. one process using > most memory with a file mmap from your fs) GFP_KERNEL can also recurse, > which can cause other problems in your fs. > > There were some changes to make this problem less severe (e.g. better > dirty pages accounting), but I don't think anyone has really declared > it solved yet. The standard workaround for this is to use mempools > for anything allocated in the writeout path, then you are at least > guaranteed to make forward progress. > > You also had at least one unchecked kmalloc I think. > > -Andi > > -- > ak@xxxxxxxxxxxxxxx -- Speaking for myself only. > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
