On Thu, Feb 13, 2020 at 08:48:47AM +0100, Michal Hocko wrote: > Can we pursue on this please? An explicit NOFS scope annotation with a > reference to compaction potentially locking up on pages in the readahead > would be a great start. How about this (on top of the current readahead series): diff --git a/mm/readahead.c b/mm/readahead.c index 29ca25c8f01e..32fd32b913da 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -160,6 +160,16 @@ unsigned long 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 migration. Telling the VM + * we're in the middle of a filesystem operation will cause it + * to not touch file-backed pages, preventing a deadlock. + */ + unsigned int nofs = memalloc_nofs_save(); + /* * Preallocate as many pages as we will need. */ @@ -217,6 +227,7 @@ unsigned long page_cache_readahead_limit(struct address_space *mapping, */ read_pages(&rac, &page_pool); BUG_ON(!list_empty(&page_pool)); + memalloc_nofs_restore(nofs); return rac.nr_pages; } EXPORT_SYMBOL_GPL(page_cache_readahead_limit);
