[PATCH 0/8] mmap_cache subsystem (re-factoring)

[Dmitry V. Levin]

On Tue, Apr 24, 2018 at 02:25:14PM +0900, Masatake YAMATO wrote:
> > On Tue, Feb 27, 2018 at 02:30:06AM +0300, Dmitry V. Levin wrote:
> >> On Sat, Jan 27, 2018 at 05:36:36AM +0900, Masatake YAMATO wrote:
> >> > When we added unwinding feature (activated with -k option), we also added
> >> > a code for caching the entries of /proc/$pid/maps.
> >> > 
> >> > The code for caching was tightly integrated with the code for
> >> > unwinding. However, while prototyping kvm vcpu state dump feature to
> >> > strace[1], I found the code for caching is useful for other purposes
> >> > than unwinding feature.
> >> > 
> >> > This patch set makes the code for caching usable independently of
> >> > unwinding feature. In the changes, I call the newly separated
> >> > code for caching "mmap_cache subsystem".
> >> > 
> >> > [1] https://marc.info/?l=kvm&m=151531408406144&w=2
> >> > 
> >> > Masatake YAMATO (8):
> >> >   unwind: lift up unw_flush_cache from mmap cache management code
> >> >   Introduce mmap_cache subsystem derived from unwind.c
> >> >   mmap_cache: Move code for searching an mmap cache from unwind
> >> >   mmap_cache: record protection bits
> >> >   Lift up mmap_cache_delete invocation from unwind.c
> >> >   mmap_cache: add function to enable mmap_cache
> >> >   mmap_cache: record device major and minor numbers
> >> >   mmap_cache: add customizable search function
> >> 
> >> Thanks, I'll merge the first 7 of them, with minor corrections
> >> (mostly related to commit messages) and a single build fix.
> > 
> > With introduction of libdw-based unwinder this mmap_cache subsystem looks
> > very odd: despite the fact that libdw-based unwinder does not use mmap_cache,
> > it's use is forced by unwind.c for no visible purpose.
> 
> mmap_cache calls tcb_flush_cache (and dwfl_linux_proc_report) when
> the memory mapping of a target process is changed.

Well, it's not mmap_cache.c but unwind.c that calls tcb_flush_cache.
Generic unwind uses just the return code of mmap_cache_rebuild_if_invalid.

mmap_cache_rebuild_if_invalid calls build_mmap_cache but the mmap cache
it builds is not used because the sole user of mmap_cache_search is
unwind-libunwind.c, all the rest don't need any mmap cache any more.


-- 
ldv
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