On Fri, Aug 11, 2023 at 03:57:05AM +0000, Hui Zhu wrote: > Encountered an issue where a large number of filesystem reads and writes > occurred suddenly within a container. At the same time, other tasks on > the same host that were performing filesystem read and write operations > became blocked. It was observed that many of the blocked tasks were > blocked on the ext4 journal lock. For example: > PID: 171453 TASK: ffff926566c9440 CPU: 54 COMMAND: "Thread" > > Meanwhile, it was observed that the task holding the ext4 journal lock > was blocked for an extended period of time on "shrink_page_list" due to > "ext4_sb_breadahead_unmovable". > > The function "grow_dev_page" increased the gfp mask with "__GFP_NOFAIL", > causing longer blocking times. > /* > * XXX: __getblk_slow() can not really deal with failure and > * will endlessly loop on improvised global reclaim. Prefer > * looping in the allocator rather than here, at least that > * code knows what it's doing. > */ > gfp_mask |= __GFP_NOFAIL; > However, "ext4_sb_breadahead_unmovable" is a prefetch function and > failures are acceptable. That's a really good point. > Therefore, this commit changes "ext4_sb_breadahead_unmovable" to be > non-blocking, removing "__GFP_DIRECT_RECLAIM" from the gfp mask in the > "grow_dev_page" function if caller is ext4_sb_breadahead_unmovable to > alleviate memory-related blocking issues. Uh, not like this though. Fix the gfp flags in the callers instead of working this new "bool" flag through the buffer head layers.
