2020년 3월 13일 (금) 오전 2:07, Roman Gushchin <guro@xxxxxx>님이 작성: > > On Thu, Mar 12, 2020 at 05:56:34PM +0900, Joonsoo Kim wrote: > > 2020년 3월 12일 (목) 오전 11:40, Roman Gushchin <guro@xxxxxx>님이 작성: > > > > > > On Thu, Mar 12, 2020 at 10:41:28AM +0900, Joonsoo Kim wrote: > > > > Hello, Roman. > > > > > > Hello, Joonsoo! > > > > > > > > > > > 2020년 3월 12일 (목) 오전 2:35, Roman Gushchin <guro@xxxxxx>님이 작성: > > > > > > > > > > On Wed, Mar 11, 2020 at 09:51:07AM +0100, Vlastimil Babka wrote: > > > > > > On 3/6/20 9:01 PM, Rik van Riel wrote: > > > > > > > Posting this one for Roman so I can deal with any upstream feedback and > > > > > > > create a v2 if needed, while scratching my head over the next piece of > > > > > > > this puzzle :) > > > > > > > > > > > > > > ---8<--- > > > > > > > > > > > > > > From: Roman Gushchin <guro@xxxxxx> > > > > > > > > > > > > > > Currently a cma area is barely used by the page allocator because > > > > > > > it's used only as a fallback from movable, however kswapd tries > > > > > > > hard to make sure that the fallback path isn't used. > > > > > > > > > > > > Few years ago Joonsoo wanted to fix these kinds of weird MIGRATE_CMA corner > > > > > > cases by using ZONE_MOVABLE instead [1]. Unfortunately it was reverted due to > > > > > > unresolved bugs. Perhaps the idea could be resurrected now? > > > > > > > > > > Hi Vlastimil! > > > > > > > > > > Thank you for this reminder! I actually looked at it and also asked Joonsoo in private > > > > > about the state of this patch(set). As I understand, Joonsoo plans to resubmit > > > > > it later this year. > > > > > > > > > > What Rik and I are suggesting seems to be much simpler, however it's perfectly > > > > > possible that Joonsoo's solution is preferable long-term. > > > > > > > > > > So if the proposed patch looks ok for now, I'd suggest to go with it and return > > > > > to this question once we'll have a new version of ZONE_MOVABLE solution. > > > > > > > > Hmm... utilization is not the only matter for CMA user. The more > > > > important one is > > > > success guarantee of cma_alloc() and this patch would have a bad impact on it. > > > > > > > > A few years ago, I have tested this kind of approach and found that increasing > > > > utilization increases cma_alloc() failure. Reason is that the page > > > > allocated with > > > > __GFP_MOVABLE, especially, by sb_bread(), is sometimes pinned by someone. > > > > > > > > Until now, cma memory isn't used much so this problem doesn't occur easily. > > > > However, with this patch, it would happen. > > > > > > Sure, but the whole point of cma is to be able to use the cma area > > > effectively by movable pages. Otherwise we can just reserve it and > > > have 100% reliability. > > > > I agree with that cma area should be used effectively. However, cma_alloc() > > failure is functional failure in embedded system so we need to approach > > this problem more carefully. At least, to control the behaviour, configurable > > option (default is current behaviour) would be necessary. > > Do we know who can test it? Adding a configuration option is a last resort > measure, I really hope we can avoid it. I don't know. Agreed that configuration option is a last resort. > > > > > So I'd focus on fixing page migration issues, rather than trying > > > to keep it empty most of the time. > > > > Great! Fixing page migration issue is always good thing! > > > > > Btw, I've fixed two issues, which dramatically increased the success > > > rate of 1 GB page allocation in my case: > > > > > > https://patchwork.kernel.org/patch/11420997/ > > > https://lore.kernel.org/patchwork/patch/1202868/ > > > > > > (They both are on the way to upstream, but not there yet) > > > > > > Can you, please, pull them and try? > > > > Unfortunately, I lose my test setup for this problem so cannot try it now. > > I will try it as soon as possible. > > Thanks! Looking forward to it... > > > > > Anyway, AFAIR, I saw the problem while journal is continually working > > on ext4. Have you checked this case? > > My ext4 fix sounds very similar to what you're describing, but it's hard to > say for sure. Okay, I will test it. Thanks.
