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! > -- > Mike Kravetz
