On Fri, Jan 26, 2018 at 12:14:40PM +0100, Marek Szyprowski wrote: > glibc in calls cacheflush syscall on the whole textrels section of the > relocated binaries. However, relocation usually doesn't touch all pages > of that section, so not all of them are read to memory when calling this > syscall. However flush_cache_user_range() function will unconditionally > touch all pages from the provided range, resulting additional overhead > related to reading all clean pages. Optimize this by calling > flush_cache_user_range() only on the pages that are already in the > memory.
What ensures that another CPU doesn't remove a page while we're flushing it? That will trigger a data abort, which will want to take the mmap_sem, causing a deadlock. > > Signed-off-by: Marek Szyprowski <[email protected]> > --- > arch/arm/kernel/traps.c | 25 +++++++++++++++++++------ > 1 file changed, 19 insertions(+), 6 deletions(-) > > diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c > index 5e3633c24e63..a5ec262ab30e 100644 > --- a/arch/arm/kernel/traps.c > +++ b/arch/arm/kernel/traps.c > @@ -564,23 +564,36 @@ static int bad_syscall(int n, struct pt_regs *regs) > static inline int > __do_cache_op(unsigned long start, unsigned long end) > { > - int ret; > + struct vm_area_struct *vma = NULL; > + int ret = 0; > > + down_read(¤t->mm->mmap_sem); > do { > unsigned long chunk = min(PAGE_SIZE, end - start); > > + if (!vma || vma->vm_end <= start) { > + vma = find_vma(current->mm, start); > + if (!vma) { > + ret = -EFAULT; > + goto done; > + } > + } > + > if (fatal_signal_pending(current)) > return 0; > > - ret = flush_cache_user_range(start, start + chunk); > - if (ret) > - return ret; > + if (follow_page(vma, start, 0)) { > + ret = flush_cache_user_range(start, start + chunk); > + if (ret) > + goto done; > + } > > cond_resched(); > start += chunk; > } while (start < end); > - > - return 0; > +done: > + up_read(¤t->mm->mmap_sem); > + return ret; > } > > static inline int > -- > 2.15.0 > -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up
