On 3/22/21 11:10 AM, Roman Gushchin wrote: > On Mon, Mar 22, 2021 at 10:42:23AM -0700, Mike Kravetz wrote: >> Cc: Roman, Christoph >> >> On 3/22/21 1:41 AM, Peter Zijlstra wrote: >>> On Fri, Mar 19, 2021 at 03:42:08PM -0700, Mike Kravetz wrote: >>>> The locks acquired in free_huge_page are irq safe. However, in certain >>>> circumstances the routine update_and_free_page could sleep. Since >>>> free_huge_page can be called from any context, it can not sleep. >>>> >>>> Use a waitqueue to defer freeing of pages if the operation may sleep. A >>>> new routine update_and_free_page_no_sleep provides this functionality >>>> and is only called from free_huge_page. >>>> >>>> Note that any 'pages' sent to the workqueue for deferred freeing have >>>> already been removed from the hugetlb subsystem. What is actually >>>> deferred is returning those base pages to the low level allocator. >>> >>> So maybe I'm stupid, but why do you need that work in hugetlb? Afaict it >>> should be in cma_release(). >> >> My thinking (which could be totally wrong) is that cma_release makes no >> claims about calling context. From the code, it is pretty clear that it >> can only be called from task context with no locks held. Although, >> there could be code incorrectly calling it today hugetlb does. Since >> hugetlb is the only code with this new requirement, it should do the >> work. >> >> Wait!!! That made me remember something. >> Roman had code to create a non-blocking version of cma_release(). >> https://lore.kernel.org/linux-mm/20201022225308.2927890-1-guro@xxxxxx/ >> >> There were no objections, and Christoph even thought there may be >> problems with callers of dma_free_contiguous. >> >> Perhaps, we should just move forward with Roman's patches to create >> cma_release_nowait() and avoid this workqueue stuff? > > Sounds good to me. If it's the preferred path, I can rebase and resend > those patches (they been carried for some time by Zi Yan for his 1GB THP work, > but they are completely independent). Thanks Roman, Yes, this is the preferred path. If there is a non blocking version of cma_release, then it makes fixup of hugetlb put_page path much easier. If you would prefer, I can rebase your patches and send with this series. -- Mike Kravetz
