In try_preserve_large_page(), the check for pgprot_val(new_prot) == pgprot_val(old_port) can definitely be done at first to avoid redundant checking.
The approach and some of the comments came from Thomas Gleixner's email example for how to do this Suggested-by: Thomas Gleixner <[email protected]> Signed-off-by: Bin Yang <[email protected]> --- arch/x86/mm/pageattr.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 8d6c34f..68613fd 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -629,6 +629,22 @@ try_preserve_large_page(pte_t *kpte, unsigned long address, new_prot = static_protections(req_prot, address, pfn); /* + * The static_protections() is used to check specific protection flags + * for certain areas of memory. The old pgprot should be checked already + * when it was applied before. If it's not, then this is a bug in some + * other code and needs to be fixed there. + * + * If new pgprot is same as old pgprot, return directly without any + * additional checking. The following static_protections() checking is + * pointless if pgprot has no change. It can avoid the redundant + * checking and optimize the performance of large page split checking. + */ + if (pgprot_val(new_prot) == pgprot_val(old_prot)) { + do_split = 0; + goto out_unlock; + } + + /* * We need to check the full range, whether * static_protection() requires a different pgprot for one of * the pages in the range we try to preserve: @@ -642,14 +658,6 @@ try_preserve_large_page(pte_t *kpte, unsigned long address, goto out_unlock; } - /* - * If there are no changes, return. maxpages has been updated - * above: - */ - if (pgprot_val(new_prot) == pgprot_val(old_prot)) { - do_split = 0; - goto out_unlock; - } /* * We need to change the attributes. Check, whether we can -- 2.7.4
