Messages in this thread | | | Date | Mon, 30 Nov 2009 11:18:06 +0800 | From | Jie Zhang <> | Subject | Re: avoiding duplicate icache flushing of shared maps on nommu |
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On 11/28/2009 11:40 PM, Mike Frysinger wrote: > when working with FDPIC, there are many shared maps of read only text > regions (the C library, applet packages like busybox, ...) between > applications. but the current mm/nommu.c:do_mmap_pgoff() function > will issue an icache flush whenever a vma is added to a mm instead of > only doing it when the map is initially created. am i missing > something obvious here, or would a change like below be OK ? this > easily cuts the number of icache flushes during boot by 50% if not > more. > > (yes, this now does the icache flush while holding the > nommu_region_sem, but i'm interested if the _idea_ is OK) > I don't see any problem. But I'm not a kernel expert. I tried to take a look at the source code history. But I cannot find code older than 2.6.12. In the CVS repository of uClinux, there is no similar code in kernel sub-directory. :-(
Jie
> --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -1409,14 +1409,14 @@ unsigned long do_mmap_pgoff(struct file *file, > > current->mm->total_vm += len>> PAGE_SHIFT; > > + if (prot& PROT_EXEC) > + flush_icache_range(result, result + len); > + > share: > add_vma_to_mm(current->mm, vma); > > up_write(&nommu_region_sem); > > - if (prot& PROT_EXEC) > - flush_icache_range(result, result + len); > - > kleave(" = %lx", result); > return result; > > -mike
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