Messages in this thread | | | Date | Wed, 1 Sep 2021 13:07:42 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v2 0/9] Free user PTE page table pages |
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On Wed, Sep 01, 2021 at 02:32:08PM +0200, David Hildenbrand wrote:
> b) pmd_trans_unstable_or_pte_try_get() and friends are really ugly.
I suspect the good API here is really more like:
ptep = pte_try_map(pmdp, &pmd_value) if (!ptep) { // pmd_value is guarenteed to not be a PTE table pointer. if (pmd_XXX(pmd_value)) }
Ie the core code will do whatever stuff, including the THP data race avoidance, to either return the next level page table or the value of a pmd that is not a enxt level page table. Callers are much clearer in this way.
Eg this is a fairly representative sample user:
static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, struct mm_walk *walk) { if (pmd_trans_unstable(pmd)) goto out; pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
And it is obviously pretty easy to integrate any refcount into pte_try_map and pte_unmap as in my other email.
Jason
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