On Tue, Jun 15, 2010 at 06:14:19PM +0200, Andrea Arcangeli wrote: > On Tue, Jun 15, 2010 at 04:38:38PM +0100, Mel Gorman wrote: > > That is pretty much what Dave is claiming here at > > http://lkml.org/lkml/2010/4/13/121 where if mempool_alloc_slab() needed > > This stack trace shows writepage called by shrink_page_list... that > contradict Christoph's claim that xfs already won't writepage if > invoked by direct reclaim. We only recently did that - before that we tried to get the VM fixed multiple times but finally had to bite the bullet and follow ext4 and btrfs in that regard. > Again not what looks like from the stack trace. Also grepping for > PF_MEMALLOC in fs/xfs shows nothing. In fact it's ext4_write_inode > that skips the write if PF_MEMALLOC is set, not writepage apparently > (only did a quick grep so I might be wrong). I suspect > ext4_write_inode is the case I just mentioned about slab shrink, not > ->writepage ;). ext4 in fact does not check PF_MEMALLOC but simply refuses to write out anything in ->writepage in most cases. There is a corner case when the page doesn't have any buffers attached where it wouldn't have write out data, without actually calling the allocator. I suspect this code actually is a leftover as we don't normally strip buffers from a page that had them before. > inodes are small, it's no big deal to keep an inode pinned and not > slab-reclaimable because dirty, while skipping real writepage in > memory pressure could really open a regression in oom false positives! > One pagecache much bigger than one inode and there can be plenty more > dirty pagecache than inodes. At least for XFS ->write_inode is really simple these days. If it's a synchronous writeout, which won't happen from these path it logs the inode, which is far less harmless than the whole allocator code, and for write = 0 it only adds it to the delayed write queue, which doesn't call into the I/O stack at all. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>