In message <200712121638.35167.nickpiggin@xxxxxxxxxxxx>, Nick Piggin writes: > On Monday 10 December 2007 13:42, Erez Zadok wrote: > > Needed to maintain cache coherency after branch management. > > > > Hmm, I'd much prefer to be able to sleep in invalidate_mapping_pages > before this function gets exported. > > As it is, it can cause massive latencies on preemption and the inode_lock > so it is pretty much debug-only IMO. I'd rather it didn't escape into the > wild as is. > > Either that or rework your cache coherency somehow. Nick, thanks for the advice. We use a generation number after each successful branch configuration command, so that ->d_revalidate later on can discover that change, and rebuild the union of objects. At ->remount time, I figured it'd be nice to "encourage" that revalidation to happen sooner, by invalidating as many upper pages as possible, thus causing ->d_revalidate/->readpage to take place sooner. So we used to call drop_pagecache_sb from our remount code: it was the only caller of drop_pagecache_sb. It wasn't too much of an latency issue to call drop_pagecache_sb there: the VFS remount code path is already pretty slow (dropping temporarily to readonly mode, and dropping other caches), and remount isn't an operation used often, so a little bit more latency would probably not have been noticed by users. Nevertheless, it was not strictly necessary to call drop_pagecache_sb in unionfs_remount, because the objects in question will have gotten revalidated sooner or later anyway; the call to drop_pagecache_sb was just an optimization (one which I wasn't 100% sure about anyway, as per my long "XXX" comment above that call in unionfs_remount). So I agree with you: if this symbol can be abused by modules and cause problems, then exporting it to modules is too risky. I've reworked my code to avoid calling drop_pagecache_sb and I'll [sic] drop that patch. Cheers, Erez. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
