On Mon, Sep 12, 2016 at 3:09 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > On Sun, Sep 11, 2016 at 10:31:35AM -0700, Dan Williams wrote: >> As evidenced by this bug report [1], userspace libraries are interested >> in whether a mapping is DAX mapped, i.e. no intervening page cache. >> Rather than using the ambiguous VM_MIXEDMAP flag in smaps, provide an >> explicit "is dax" indication as a new flag in the page vector populated >> by mincore. >> >> There are also cases, particularly for testing and validating a >> configuration to know the hardware mapping geometry of the pages in a >> given process address range. Consider filesystem-dax where a >> configuration needs to take care to align partitions and block >> allocations before huge page mappings might be used, or >> anonymous-transparent-huge-pages where a process is opportunistically >> assigned large pages. mincore2() allows these configurations to be >> surveyed and validated. >> >> The implementation takes advantage of the unused bits in the per-page >> byte returned for each PAGE_SIZE extent of a given address range. The >> new format of each vector byte is: >> >> (TLB_SHIFT - PAGE_SHIFT) << 2 | vma_is_dax() << 1 | page_present >> >> [1]: https://lkml.org/lkml/2016/9/7/61 >> >> Cc: Arnd Bergmann <arnd@xxxxxxxx> >> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> >> Cc: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx> >> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> >> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> >> --- >> include/linux/syscalls.h | 2 + >> include/uapi/asm-generic/mman-common.h | 3 + >> kernel/sys_ni.c | 1 >> mm/mincore.c | 126 +++++++++++++++++++++++++------- >> 4 files changed, 104 insertions(+), 28 deletions(-) >> >> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h >> index d02239022bd0..4aa2ee7e359a 100644 >> --- a/include/linux/syscalls.h >> +++ b/include/linux/syscalls.h >> @@ -467,6 +467,8 @@ asmlinkage long sys_munlockall(void); >> asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior); >> asmlinkage long sys_mincore(unsigned long start, size_t len, >> unsigned char __user * vec); >> +asmlinkage long sys_mincore2(unsigned long start, size_t len, >> + unsigned char __user * vec, int flags); > > We had few attempts to extand mincore(2) interface/functionality before. > None of them ended up in upsteam. > > How this attempt compares to previous? Not sure, I'm wading into this cold trying to get my pet problem solved, hence the RFC. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
