From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Ensure that memory allocations in the readahead path do not attempt to reclaim file-backed pages, which could lead to a deadlock. It is possible, though unlikely this is the root cause of a problem observed by Cong Wang. Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reported-by: Cong Wang <xiyou.wangcong@xxxxxxxxx> Suggested-by: Michal Hocko <mhocko@xxxxxxxx> --- mm/readahead.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/readahead.c b/mm/readahead.c index 94d499cfb657..8f9c0dba24e7 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -22,6 +22,7 @@ #include <linux/mm_inline.h> #include <linux/blk-cgroup.h> #include <linux/fadvise.h> +#include <linux/sched/mm.h> #include "internal.h" @@ -174,6 +175,18 @@ void page_cache_readahead_limit(struct address_space *mapping, ._nr_pages = 0, }; + /* + * Partway through the readahead operation, we will have added + * locked pages to the page cache, but will not yet have submitted + * them for I/O. Adding another page may need to allocate memory, + * which can trigger memory reclaim. Telling the VM we're in + * the middle of a filesystem operation will cause it to not + * touch file-backed pages, preventing a deadlock. Most (all?) + * filesystems already specify __GFP_NOFS in their mapping's + * gfp_mask, but let's be explicit here. + */ + unsigned int nofs = memalloc_nofs_save(); + /* * Preallocate as many pages as we will need. */ @@ -227,6 +240,7 @@ void page_cache_readahead_limit(struct address_space *mapping, if (readahead_count(&rac)) read_pages(&rac, &page_pool); BUG_ON(!list_empty(&page_pool)); + memalloc_nofs_restore(nofs); } EXPORT_SYMBOL_GPL(page_cache_readahead_limit); -- 2.25.0
