Messages in this thread | | | Date | Thu, 9 Feb 2006 23:28:01 -0800 | From | Andrew Morton <> | Subject | Re: msync() behaviour broken for MS_ASYNC, revert patch? |
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linux@horizon.com wrote: > > > Well, no. Consider a continuously-running application which modifies its > > data store via MAP_SHARED+msync(MS_ASYNC). If the msync() immediately > > started I/O, the disk would be seeking all over the place all the time. The > > queue merging and timer-based unplugging would help here, but it won't be > > as good as a big, infrequent ascending-file-offset pdflush pass. > > > > Secondly, consider the behaviour of the above application if it is modifying > > the same page relatively frequently (quite likely). If MS_ASYNC starts I/O > > immediately, that page will get written 10, 100 or 1000 times per second. > > If MS_ASYNC leaves it to pdflush, that page gets written once per 30 > > seconds, so we do far much less I/O. > > You're assuming a brain-dead application.
We've covered this. Handing pte-dirty pages over to pdflush for prompt writeback is a perfectly valid, sensible and fast thing to do.
It efficiently solves the single biggest problem with using MAP_SHARED instead of write().
> As I said, I'm actively looking for a way, on Linux 2.6.x, x <= 15, > to start disk writes on part of an mmapped file without either blocking > (yet)
I cannot think of a way, sorry.
> or writing other dirty pages that aren't complete yet.
msync() will write all of the file's dirty pages and it has always has done that. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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