On Fri, Aug 13, 2021 at 02:05:10PM +0800, Guoqing Jiang wrote: > From: Guoqing Jiang <jiangguoqing@xxxxxxxxxx> > > We can't split bio with more than BIO_MAX_VECS sectors, otherwise the > below call trace was triggered because we could allocate oversized > write behind bio later. > > [ 8.097936] bvec_alloc+0x90/0xc0 > [ 8.098934] bio_alloc_bioset+0x1b3/0x260 > [ 8.099959] raid1_make_request+0x9ce/0xc50 [raid1] Which bio_alloc_bioset is this? The one in alloc_behind_master_bio? In which case I think you want to limit the reduction of max_sectors to just the write behind case, and clearly document what is going on. In general the size of a bio only depends on the number of vectors, not the total I/O size. But alloc_behind_master_bio allocates new backing pages using order 0 allocations, so in this exceptional case the total size oes actually matter. While we're at it: this huge memory allocation looks really deadlock prone.
