Messages in this thread | | | From | Holger Hoffstätte <> | Subject | Re: [PATCHSET v3][RFC] Make background writeback not suck | Date | Thu, 31 Mar 2016 22:09:56 +0000 (UTC) |
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Hi,
Jens mentioned on Twitter I should post my experience here as well, so here we go.
I've backported this series (incl. updates) to stable-4.4.x - not too difficult, minus the NVM part which I don't need anyway - and have been running it for the past few days without any problem whatsoever, with GREAT success.
My use case is primarily larger amounts of stuff (transcoded movies, finished downloads, built Gentoo packages) that gets copied from tmpfs to SSD (or disk) and every time that happens, the system noticeably strangles readers (desktop, interactive shell). It does not really matter how I tune writeback via the write_expire/dirty_bytes knobs or the scheduler (and yes, I understand how they work); lowering the writeback limits helped a bit but the system is still overwhelmed. Jacking up deadline's writes_starved to unreasonable levels helps a bit, but in turn makes all writes suffer. Anything else - even tried BFQ for a while, which has its own unrelated problems - didn't really help either.
With this patchset the buffered writeback in these situations is much improved, and copying several GBs at once to a SATA-3 SSD (or even an external USB-2 disk with measly 40 MB/s) doodles along in the background like it always should have, and desktop work is not noticeably affected.
I guess the effect will be even more noticeable on slower block devices (laptops, old SSDs or disks).
So: +1 would apply again!
cheers Holger
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