On Wed, 7 Oct 2015, David Zafman wrote: > > There would be a benefit to doing fadvise POSIX_FADV_DONTNEED after > deep-scrub reads for objects not recently accessed by clients. Yeah, it's the 'except for stuff already in cache' part that we don't do (and the kernel doesn't give us a good interface for). IIRC there was a patch that guessed based on whether the obc was already in cache, which seems like a pretty decent heuristic, but I forget if that was in the final version. > I see the NewStore objectstore sometimes using the O_DIRECT flag for writes. > This concerns me because the open(2) man pages says: > > "Applications should avoid mixing O_DIRECT and normal I/O to the same file, > and especially to overlapping byte regions in the same file. Even when the > filesystem correctly handles the coherency issues in this situation, overall > I/O throughput is likely to be slower than using either mode alone." Yeah: an O_DIRECT write will do a cache flush on the write range, so if there was already dirty data in cache you'll write twice. There's similarly an invalidate on read. I need to go back through the newstore code and see how the modes are being mixed and how it can be avoided... sage > > David > > On 10/7/15 7:50 AM, Sage Weil wrote: > > It's not, but it would not be ahrd to do this. There are fadvise-style > > hints being passed down that could trigger O_DIRECT reads in this case. > > That may not be the best choice, though--it won't use data that happens > > to be in cache and it'll also throw it out.. > > > > On Wed, 7 Oct 2015, Pawe? Sadowski wrote: > > > > > Hi, > > > > > > Can anyone tell if deep scrub is done using O_DIRECT flag or not? I'm > > > not able to verify that in source code. > > > > > > If not would it be possible to add such feature (maybe config option) to > > > help keeping Linux page cache in better shape? > > > > > > Thanks, > > > > > > -- > > > PS > > > > > > _______________________________________________ > > > ceph-users mailing list > > > ceph-users@xxxxxxxxxxxxxx > > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > > > > > > -- > > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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