On Thu, 28 Nov 2013 16:48:43 +0900 Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
> Now, we have an infrastructure in rmap_walk() to handle difference
> from variants of rmap traversing functions.
>
> So, just use it in try_to_unmap().
>
> In this patch, I change following things.
>
> 1. enable rmap_walk() if !CONFIG_MIGRATION.
> 2. mechanical change to use rmap_walk() in try_to_unmap().
>
> ...
>
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -190,7 +190,7 @@ int page_referenced_one(struct page *, struct vm_area_struct *,
>
> int try_to_unmap(struct page *, enum ttu_flags flags);
> int try_to_unmap_one(struct page *, struct vm_area_struct *,
> - unsigned long address, enum ttu_flags flags);
> + unsigned long address, void *arg);
This change is ugly and unchangelogged.
Also, "enum ttu_flags flags" was nice and meaningful, but "void *arg"
conveys far less information. A suitable way to address this
shortcoming is to document `arg' at the try_to_unmap_one() definition
site. try_to_unmap_one() doesn't actually have any documentation at
this stage - let's please fix that?
>
> ...
>
> @@ -1509,6 +1510,11 @@ bool is_vma_temporary_stack(struct vm_area_struct *vma)
> return false;
> }
>
> +static int skip_vma_temporary_stack(struct vm_area_struct *vma, void *arg)
> +{
> + return (int)is_vma_temporary_stack(vma);
> +}
The (int) cast is unneeded - the compiler will turn a bool into an int.
Should this function (and rmap_walk_control.skip()) really be returning
a bool?
The name of this function is poor: "skip_foo" implies that the function
will skip over a foo. But that isn't what this function does. Please
choose something which accurately reflects the function's behavior.
> /**
> * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
> * rmap method
> @@ -1554,7 +1560,7 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
> continue;
>
> address = vma_address(page, vma);
> - ret = try_to_unmap_one(page, vma, address, flags);
> + ret = try_to_unmap_one(page, vma, address, (void *)flags);
> if (ret != SWAP_AGAIN || !page_mapped(page))
> break;
> }
>
> ...
>
> /**
> * try_to_unmap - try to remove all page table mappings to a page
> * @page: the page to get unmapped
> @@ -1630,16 +1641,30 @@ out:
> int try_to_unmap(struct page *page, enum ttu_flags flags)
> {
> int ret;
> + struct rmap_walk_control rwc;
>
> - BUG_ON(!PageLocked(page));
> VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
>
> - if (unlikely(PageKsm(page)))
> - ret = try_to_unmap_ksm(page, flags);
> - else if (PageAnon(page))
> - ret = try_to_unmap_anon(page, flags);
> - else
> - ret = try_to_unmap_file(page, flags);
> + memset(&rwc, 0, sizeof(rwc));
> + rwc.main = try_to_unmap_one;
> + rwc.arg = (void *)flags;
> + rwc.main_done = page_not_mapped;
> + rwc.file_nonlinear = try_to_unmap_nonlinear;
> + rwc.anon_lock = page_lock_anon_vma_read;
struct rmap_walk_control rwc = {
...
};
> + /*
> + * During exec, a temporary VMA is setup and later moved.
> + * The VMA is moved under the anon_vma lock but not the
> + * page tables leading to a race where migration cannot
> + * find the migration ptes. Rather than increasing the
> + * locking requirements of exec(), migration skips
> + * temporary VMAs until after exec() completes.
> + */
> + if (flags & TTU_MIGRATION && !PageKsm(page) && PageAnon(page))
> + rwc.vma_skip = skip_vma_temporary_stack;
> +
> + ret = rmap_walk(page, &rwc);
> +
> if (ret != SWAP_MLOCK && !page_mapped(page))
> ret = SWAP_SUCCESS;
> return ret;
>
> ...
>
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