On Wed, 2013-10-23 at 02:53 -0700, wal...@google.com wrote: > On Sun, Oct 20, 2013 at 08:26:15PM -0700, Davidlohr Bueso wrote: > > From: Davidlohr Bueso <davidl...@hp.com> > > Subject: [PATCH v2 3/3] vdso: preallocate new vmas > > > > With the exception of um and tile, architectures that use > > the install_special_mapping() function, when setting up a > > new vma at program startup, do so with the mmap_sem lock > > held for writing. Unless there's an error, this process > > ends up allocating a new vma through kmem_cache_zalloc, > > and inserting it in the task's address space. > > > > This patch moves the vma's space allocation outside of > > install_special_mapping(), and leaves the callers to do so > > explicitly, without depending on mmap_sem. The same goes for > > freeing: if the new vma isn't used (and thus the process fails > > at some point), it's caller's responsibility to free it - > > currently this is done inside install_special_mapping. > > > > Furthermore, uprobes behaves exactly the same and thus now the > > xol_add_vma() function also preallocates the new vma. > > > > While the changes to x86 vdso handling have been tested on both > > large and small 64-bit systems, the rest of the architectures > > are totally *untested*. Note that all changes are quite similar > > from architecture to architecture. > > > > Signed-off-by: Davidlohr Bueso <davidl...@hp.com> > > Cc: Russell King <li...@arm.linux.org.uk> > > Cc: Catalin Marinas <catalin.mari...@arm.com> > > Cc: Will Deacon <will.dea...@arm.com> > > Cc: Richard Kuo <r...@codeaurora.org> > > Cc: Ralf Baechle <r...@linux-mips.org> > > Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org> > > Cc: Paul Mackerras <pau...@samba.org> > > Cc: Martin Schwidefsky <schwidef...@de.ibm.com> > > Cc: Heiko Carstens <heiko.carst...@de.ibm.com> > > Cc: Paul Mundt <let...@linux-sh.org> > > Cc: Chris Metcalf <cmetc...@tilera.com> > > Cc: Jeff Dike <jd...@addtoit.com> > > Cc: Richard Weinberger <rich...@nod.at> > > Cc: Thomas Gleixner <t...@linutronix.de> > > Cc: Ingo Molnar <mi...@redhat.com> > > Cc: "H. Peter Anvin" <h...@zytor.com> > > Cc: Peter Zijlstra <a.p.zijls...@chello.nl> > > --- > > v2: > > - Simplify install_special_mapping interface (Linus Torvalds) > > - Fix return for uml_setup_stubs when mem allocation fails (Richard > > Weinberger) > > I'm still confused as to why you're seeing any gains with this > one. This code runs during exec when mm isn't shared with any other > threads yet, so why does it matter how long the mmap_sem is held since > nobody else can contend on it ? (well, except for accesses from > /fs/proc/base.c, but I don't see why these would matter in your > benchmarks either).
Yeah, that's why I dropped the performance numbers from the changelog in v2, of course any differences are within the noise range. When I did the initial runs I was scratching my head as to why I was seeing benefits, but it was most likely a matter of clock frequency differences, and I no longer see such boosts. Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
