On Wed, 2010-08-18 at 15:34 -0400, Chris Mason wrote: > On Wed, Aug 18, 2010 at 03:04:01PM -0400, Trond Myklebust wrote: > > From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> > > > > Allowing kswapd to do GFP_KERNEL memory allocations (or any blocking memory > > allocations) is wrong and can cause deadlocks in try_to_release_page(), as > > the filesystem believes it is safe to allocate new memory and block, > > whereas kswapd is there specifically to clear a low-memory situation... > > > > Set the gfp_mask to GFP_IOFS instead. > > I always thought releasepage was supposed to do almost zero work. It > could release an instantly freeable page but it wasn't supposed to dive > in and solve world hunger or anything. > > I thought the VM would be using writepage for that. writepage isn't sufficient for the NFS case: the page may be in the 'clean but unstable' state, in which case the NFS client needs to send a COMMIT rpc call before the page can finally be released. That is why we need the gfp_flag to tell us when it is safe to do this, and when it is not. The main case where it is safe and necessary for try_to_release_page() to initiate a COMMIT call is in the invalidate_inode_pages2(). We might want to do it in the kswapd case too, but in that case, we definitely should tell the filesystem that it is unsafe to block. Trond -- 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