Hi Konstantin, Thank you very much for your detailed explanatin. I understood the policy of vmem.
Many thanks, Kohji Okuno > On Sun, Oct 05, 2014 at 01:15:12PM +0900, Kohji Okuno wrote: >> Hi, >> >> > On Sat, Oct 04, 2014 at 08:53:35PM +0900, Kohji Okuno wrote: >> >> Hi Konstantin, >> >> >> >> Thank you for your prompt response. >> >> I will test and report from next monday. >> >> >> >> >> In addtion, I have one question. >> >> >> In current and 10-stable, is vm_map_delete() called by kva_free()? >> >> > No, kva_free() only releases the vmem backing, leaving the page >> >> > tables intact. This is why I only did the stable/9 patch. >> >> >> >> Where are PTEs allocated by pmap_mapdev() freed in current and 10-stable? >> >> Could you please explain me? >> > They are not freed. The removal of the vmem which covers the address >> > space managed by corresponding ptes, allows the reuse of both KVA region >> > and corresponding PTEs in the tables. The only concern with the resident >> > page tables is to avoid two kva_alloc() to step over each other, and >> > this is ensured by vmem. >> >> I agree that normal pages are reusable. But, since the pages mapped by >> pmap_mapdev() are concerned with the physicall address of device (For >> example: video memory), these PTEs aren't reusable, I think. >> So, should we free these PTEs by pmap_unmapdev()? > There is no hold on any physical pages which were referenced by the ptes. > The only thing which is left out are the records in the page tables > which map the KVA to said device memory. It is harmless. > > When the KVA is reused, the ptes in page tables are overwritten. > > It might be argued that clearing PTEs, or at least removing the PG_V > bit catches erronous unintended accesses to the freed range, but by the > cost of the overhead of re-polluting the caches. And since clearing is > not effective without doing TLB flush, which requires broadcast IPI, > it is more trouble than advantage. > _______________________________________________ > email@example.com mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org" _______________________________________________ firstname.lastname@example.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"