| Message ID | 20210226091718.2927291-2-yuzhao@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | trim the uses of compound_head() | expand |
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index db914477057b..1995208a3763 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -248,7 +248,7 @@ static inline void page_init_poison(struct page *page, size_t size) PF_POISONED_CHECK(page); }) #define PF_NO_TAIL(page, enforce) ({ \ VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page); \ - PF_POISONED_CHECK(compound_head(page)); }) + PF_POISONED_CHECK((enforce) ? (page) : compound_head(page)); }) #define PF_NO_COMPOUND(page, enforce) ({ \ VM_BUG_ON_PGFLAGS(enforce && PageCompound(page), page); \ PF_POISONED_CHECK(page); })
When testing page flags with PF_NO_TAIL (enforce=0), tail pages are legit and they are converted by compound_head(). When modifying page flags (enforce=1), tail pages are not legit and they either trigger VM_BUG_ON_PGFLAGS() or are "corrected" by compound_head(). There is no evidence such "correction" is beneficial in terms of preventing a buggy kernel from crashing. But there is clear evidence it's detrimental to the size of vmlinux because compound_head() is redundantly inlined for all modifications of small and head page flags using PF_NO_TAIL. This patch makes PF_NO_TAIL skip compound_head() when modifying page flags. There won't be any behavior change unless a piece of buggy code tries to modify tail page flags using PF_NO_TAIL. Such code won't be "corrected", if VM_BUG_ON_PGFLAGS() isn't there to catch it. Again, there is no evidence such "correction" is beneficial. bloat-o-meter result: add/remove: 0/0 grow/shrink: 4/62 up/down: 309/-2851 (-2542) Signed-off-by: Yu Zhao <yuzhao@google.com> --- include/linux/page-flags.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)