Messages in this thread | | | Date | Fri, 04 May 2012 15:26:13 +0800 | From | Alex Shi <> | Subject | Re: [PATCH] THP: need is_vma_temporary_stack() when reference transparent_hugepage_enabled |
| |
On 05/03/2012 07:25 PM, Andrea Arcangeli wrote:
> Hi, > > On Thu, May 03, 2012 at 08:56:57AM +0800, Alex Shi wrote: >> >>> My preference would still be to remove the is_vma_temporary_stack and >>> use two vmas during mremap of execve, that would remove the "vma" >>> parameter from transparent_hugepage_enabled() but others prefers to >>> skip a vma allocation in execve and stick to is_vma_temporary_stack, >>> which is fair enough argument. >> >> >> Actually, current transparent_hugepage_enabled just means the vma is in >> THP enable ENV, the vma is just possibly has some large page, no grantee >> really has. But in lots situations, user wants to know if a vma or a >> part of memory really include a large page. not the possibility. >> >> So, it will be great to see a real large page checking function appearing. > > Well, to know if a VMA (or a memory range) really includes a THP, it'd > require to hold the page_table_lock and a loop on all pmds in the > range, but by the time you relase the lock things may have already > changed as split_huge_page can run at any time, madvise(MADV_DONTNEED) > too if you only hold the mmap_sem in read mode and the THP page > fault. In fact while holding the mmap_sem in read mode (the usual read > lock you need to take to lookup and stabilize the vma) a THP can be > freed and reallocated under it, and that's what pmd_trans_unstable is > about.
Appreciate for explanation!
| |