On Wed, Apr 04, 2007 at 12:12:11PM -0700, Jeremy Fitzhardinge wrote:
> Add a new mm function apply_to_page_range() which applies a given
> function to every pte in a given virtual address range in a given mm
> structure. This is a generic alternative to cut-and-pasting the Linux
> idiomatic pagetable walking code in every place that a sequence of
> PTEs must be accessed.
As we discussed before, this obviously has a lot in common with my
walk_page_range code.
The major difference and one your above description seems to be
missing the important detail of why it's doing this:
> + pte_alloc_kernel(pmd, addr) :
> + pmd = pmd_alloc(mm, pud, addr);
> + pud = pud_alloc(mm, pgd, addr);
..which is mentioned here:
> +/*
> + * Scan a region of virtual memory, filling in page tables as necessary
> + * and calling a provided function on each leaf page table.
> + */
But I'm not sure what the use case is that wants filling in the page
table..? If both modes really make sense, perhaps a flag could unify
these differences.
> +typedef int (*pte_fn_t)(pte_t *pte, struct page *pmd_page, unsigned long
> addr,
> + void *data);
I'd gotten the impression that these sorts of typedefs were out of
fashion.
> +static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
> + unsigned long addr, unsigned long end,
> + pte_fn_t fn, void *data)
> +{
> + pte_t *pte;
> + int err;
> + struct page *pmd_page;
> + spinlock_t *ptl;
> +
> + pte = (mm == &init_mm) ?
> + pte_alloc_kernel(pmd, addr) :
> + pte_alloc_map_lock(mm, pmd, addr, &ptl);
> + if (!pte)
> + return -ENOMEM;
Seems a bit awkward to pass mm all the way down the tree just for this
quirk. Which is a bit awkward as it means that whether or not a lock
is held in the callback is context dependent.
smaps, clear_ref, and my pagemap code all use the callback at the
pmd_range level, which a) localizes the pte-level locking concerns
with the user b) amortizes the indirection overhead and c)
(unfortunately) makes the user a bit more complex.
We should try to measure whether (b) actually makes a difference.
> + do {
> + err = fn(pte, pmd_page, addr, data);
> + if (err)
> + break;
> + } while (pte++, addr += PAGE_SIZE, addr != end);
I was about to say this do/while format seems a bit non-idiomatic for
page table walkers, but then I looked at the code in mm/memory.c and
realized the stuff I've been hacking on is the odd one out.
--
Mathematics is the supreme nostalgia of our time.
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