Hi, I noticed that after the recent "page-flags" patchset, there are an excessive number of calls to compound_head() in certain places.
For example, the frequently executed mark_page_accessed() function already starts out by calling compound_head(), but then each time it tests a page flag afterwards, there is an extra, seemingly unnecessary, call to compound_head(). This causes a series of instructions like the following to appear no fewer than 10 times throughout the function: ffffffff81119db4: 48 8b 53 20 mov 0x20(%rbx),%rdx ffffffff81119db8: 48 8d 42 ff lea -0x1(%rdx),%rax ffffffff81119dbc: 83 e2 01 and $0x1,%edx ffffffff81119dbf: 48 0f 44 c3 cmove %rbx,%rax ffffffff81119dc3: 48 8b 00 mov (%rax),%rax Part of the problem, I suppose, is that the compiler doesn't know that the pages can't be linked more than one level deep. Is this a known tradeoff, and have any possible solutions been considered? Eric
