From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: mm: move PageDoubleMap bit Patch series "Fix PageDoubleMap". This is a purely theoretical problem for now as none of the filesystems which use PG_private_2 (ie PG_fscache) are being converted at this time, but it's confusing to leave it like this. This patch (of 2): PG_private_2 is defined as being PF_ANY (applicable to tail pages as well as regular & head pages). That means that the first tail page of a double-map page will appear to have Private2 set. Use the Workingset bit instead which is defined as PF_HEAD so any attempt to access the Workingset bit on a tail page will redirect to the head page's Workingset bit. Link: https://lkml.kernel.org/r/20200629151933.15671-1-willy@xxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20200629151933.15671-2-willy@xxxxxxxxxxxxx Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/page-flags.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/include/linux/page-flags.h~mm-move-pagedoublemap-bit +++ a/include/linux/page-flags.h @@ -167,7 +167,7 @@ enum pageflags { PG_slob_free = PG_private, /* Compound pages. Stored in first tail page's flags */ - PG_double_map = PG_private_2, + PG_double_map = PG_workingset, /* non-lru isolated movable page */ PG_isolated = PG_reclaim, _
