On Wed, 2019-04-24 at 08:49 -0700, James Bottomley wrote: > On Wed, 2019-04-24 at 08:32 -0700, Bart Van Assche wrote: > > Another concern is whether this change can cause a livelock. If the > > system is running out of memory and the page cache submits a write > > request with a scatterlist with more than two elements, if the > > kmalloc() for the scatterlist fails, will that prevent the page cache > > from making any progress with writeback? > > It's pool backed, as I said. Is the concern there isn't enough depth > in the pools for a large write?
That memory pool is used by multiple drivers. Most but not all sg_alloc_table_chained() calls happen from inside .queue_rq() implementations. One sg_alloc_table_chained() call occurs in the NFS server code. I'm not sure whether it is guaranteed that an sg_alloc_table_chained() will succeed sooner or later under low memory conditions. Additionally, new sg_alloc_table_chained() could be added in drivers any time. Bart.
