Messages in this thread | | | Subject | Re: [PATCH v4] Add /proc/PID/smaps support for DAX | From | Dave Hansen <> | Date | Thu, 26 Oct 2017 07:03:01 -0700 |
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I'm honestly not understanding what problem this solves. Could you, perhaps, do a before and after of smaps with and without this patch?
> +/* page structure behind DAX mappings is NOT compound page > + * when it's a huge page mappings, so introduce new API to > + * account for both PMD and PUD mapping. > + */
Why do they need to be compound? Why don't we just make them compound instead of adding all this code which is *just* for DAX?
> +static void smaps_account_dax_huge(struct mem_size_stats *mss, > + struct page *page, unsigned long size, bool young, bool dirty) > +{ > + int mapcount = page_mapcount(page); > + > + if (PageAnon(page)) { > + mss->anonymous += size; > + if (!PageSwapBacked(page) && !dirty && !PageDirty(page)) > + mss->lazyfree += size; > + }
How can you have DAX anonymous huge pages?
> + mss->resident += size; > + /* Accumulate the size in pages that have been accessed. */ > + if (young || page_is_young(page) || PageReferenced(page)) > + mss->referenced += size;
Isn't this just a copy'n'paste of smaps_account() code?
> + /* > + * page_count(page) == 1 guarantees the page is mapped exactly once. > + * If any subpage of the compound page mapped with PTE it would elevate > + * page_count(). > + */ > + if (page_count(page) == 1) { > + if (dirty || PageDirty(page)) > + mss->private_dirty += size; > + else > + mss->private_clean += size; > + mss->pss += (u64)size << PSS_SHIFT; > + return; > + }
PSS makes *zero* sense for DAX. The "memory" is used whether the mapping exists or not.
Also, the idea of "private" doesn't really make sense here.
> + if (mapcount >= 2) { > + if (dirty || PageDirty(page)) > + mss->shared_dirty += size; > + else > + mss->shared_clean += size; > + mss->pss += (size << PSS_SHIFT) / mapcount; > + } else { > + if (dirty || PageDirty(page)) > + mss->private_dirty += size; > + else > + mss->private_clean += size; > + mss->pss += size << PSS_SHIFT; > + } > +} > + > #ifdef CONFIG_SHMEM > static int smaps_pte_hole(unsigned long addr, unsigned long end, > struct mm_walk *walk) > @@ -528,7 +577,16 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr, > struct page *page = NULL; > > if (pte_present(*pte)) { > - page = vm_normal_page(vma, addr, *pte); > + if (!vma_is_dax(vma)) > + page = vm_normal_page(vma, addr, *pte); > + else if (pte_devmap(*pte)) { > + struct dev_pagemap *pgmap; > + > + pgmap = get_dev_pagemap(pte_pfn(*pte), NULL); > + if (!pgmap) > + return; > + page = pte_page(*pte); > + } > } else if (is_swap_pte(*pte)) { > swp_entry_t swpent = pte_to_swp_entry(*pte); > > @@ -579,7 +637,19 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr, > struct page *page; > > /* FOLL_DUMP will return -EFAULT on huge zero page */ > - page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP); > + if (!vma_is_dax(vma)) > + page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP); > + else if (pmd_devmap(*pmd)) { > + struct dev_pagemap *pgmap; > + > + pgmap = get_dev_pagemap(pmd_pfn(*pmd), NULL); > + if (!pgmap) > + return; > + page = pmd_page(*pmd); > + smaps_account_dax_huge(mss, page, PMD_SIZE, pmd_young(*pmd), > + pmd_dirty(*pmd)); > + return; > + } > if (IS_ERR_OR_NULL(page)) > return; > if (PageAnon(page)) >
There's a fair amount of copying and pasting going on here. There is, again, a bunch of specialized DAX code. Isn't there a way to do this more generically?
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