Messages in this thread | | | Subject | Re: [PATCH rfc 0/2] mm: cma: make cma_release() non-blocking | From | "Xiaqing (A)" <> | Date | Thu, 22 Oct 2020 11:47:46 +0800 |
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On 2020/10/22 10:45, Roman Gushchin wrote:
> On Thu, Oct 22, 2020 at 09:54:53AM +0800, Xiaqing (A) wrote: >> >> On 2020/10/17 6:52, Roman Gushchin wrote: >> >>> This small patchset makes cma_release() non-blocking and simplifies >>> the code in hugetlbfs, where previously we had to temporarily drop >>> hugetlb_lock around the cma_release() call. >>> >>> It should help Zi Yan on his work on 1 GB THPs: splitting a gigantic >>> THP under a memory pressure requires a cma_release() call. If it's >>> a blocking function, it complicates the already complicated code. >>> Because there are at least two use cases like this (hugetlbfs is >>> another example), I believe it's just better to make cma_release() >>> non-blocking. >>> >>> It also makes it more consistent with other memory releasing functions >>> in the kernel: most of them are non-blocking. >>> >>> >>> Roman Gushchin (2): >>> mm: cma: make cma_release() non-blocking >>> mm: hugetlb: don't drop hugetlb_lock around cma_release() call >>> >>> mm/cma.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++-- >>> mm/hugetlb.c | 6 ------ >>> 2 files changed, 49 insertions(+), 8 deletions(-) >>> >> I don't think this patch is a good idea.It transfers part or even all of the time of >> cma_release to cma_alloc, which is more concerned by performance indicators. > I'm not quite sure: if cma_alloc() is racing with cma_release(), cma_alloc() will > wait for the cma_lock mutex anyway. So we don't really transfer anything to cma_alloc(). > >> On Android phones, CPU resource competition is intense in many scenarios, >> As a result, kernel threads and workers can be scheduled only after some ticks or more. >> In this case, the performance of cma_alloc will deteriorate significantly, >> which is not good news for many services on Android. > Ok, I agree, if the cpu is heavily loaded, it might affect the total execution time. > > If we aren't going into the mutex->spinlock conversion direction (as Mike suggested), > we can address the performance concerns by introducing a cma_release_nowait() function, > so that the default cma_release() would work in the old way. > cma_release_nowait() can set an atomic flag on a cma area, which will cause following > cma_alloc()'s to flush the release queue. In this case there will be no performance > penalty unless somebody is using cma_release_nowait(). > Will it work for you?
That looks good to me.
Thanks!
> > Thank you! > >
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