On Fri, Mar 21, 2014 at 2:17 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
> This patch adds the hooks in the vmscan logic to discard volatile pages
> and mark their pte as purged. With this, volatile pages will be purged
> under pressure, and their ptes swap entry's marked. If the purged pages
> are accessed before being marked non-volatile, we catch this and send a
> SIGBUS.
>
> This is a simplified implementation that uses logic from Minchan's earlier
> efforts, so credit to Minchan for his work.
>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Robert Love <rlove@xxxxxxxxxx>
> Cc: Mel Gorman <mel@xxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Dave Hansen <dave@xxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>
> Cc: Neil Brown <neilb@xxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Mike Hommey <mh@xxxxxxxxxxxx>
> Cc: Taras Glek <tglek@xxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx>
> Cc: Michel Lespinasse <walken@xxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx <linux-mm@xxxxxxxxx>
> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> ---
> include/linux/vrange.h | 2 +
> mm/internal.h | 2 -
> mm/memory.c | 21 +++++++++
> mm/rmap.c | 5 +++
> mm/vmscan.c | 12 ++++++
> mm/vrange.c | 114 +++++++++++++++++++++++++++++++++++++++++++++++++
> 6 files changed, 154 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/vrange.h b/include/linux/vrange.h
> index 986fa85..d93ad21 100644
> --- a/include/linux/vrange.h
> +++ b/include/linux/vrange.h
> @@ -8,4 +8,6 @@
> #define VRANGE_VOLATILE 1
> #define VRANGE_VALID_FLAGS (0) /* Don't yet support any flags */
>
> +extern int discard_vpage(struct page *page);
> +
> #endif /* _LINUX_VRANGE_H */
> diff --git a/mm/internal.h b/mm/internal.h
> index 29e1e76..ea66bf9 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -225,10 +225,8 @@ static inline void mlock_migrate_page(struct page *newpage, struct page *page)
>
> extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
>
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> extern unsigned long vma_address(struct page *page,
> struct vm_area_struct *vma);
> -#endif
> #else /* !CONFIG_MMU */
> static inline int mlocked_vma_newpage(struct vm_area_struct *v, struct page *p)
> {
> diff --git a/mm/memory.c b/mm/memory.c
> index 22dfa61..db5f4da 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -60,6 +60,7 @@
> #include <linux/migrate.h>
> #include <linux/string.h>
> #include <linux/dma-debug.h>
> +#include <linux/vrange.h>
>
> #include <asm/io.h>
> #include <asm/pgalloc.h>
> @@ -3643,6 +3644,8 @@ static int handle_pte_fault(struct mm_struct *mm,
>
> entry = *pte;
> if (!pte_present(entry)) {
> + swp_entry_t vrange_entry;
> +retry:
> if (pte_none(entry)) {
> if (vma->vm_ops) {
> if (likely(vma->vm_ops->fault))
> @@ -3652,6 +3655,24 @@ static int handle_pte_fault(struct mm_struct *mm,
> return do_anonymous_page(mm, vma, address,
> pte, pmd, flags);
> }
> +
> + vrange_entry = pte_to_swp_entry(entry);
> + if (unlikely(is_vpurged_entry(vrange_entry))) {
> + if (vma->vm_flags & VM_VOLATILE)
> + return VM_FAULT_SIGBUS;
> +
> + /* zap pte */
> + ptl = pte_lockptr(mm, pmd);
> + spin_lock(ptl);
> + if (unlikely(!pte_same(*pte, entry)))
> + goto unlock;
> + flush_cache_page(vma, address, pte_pfn(*pte));
> + ptep_clear_flush(vma, address, pte);
> + pte_unmap_unlock(pte, ptl);
> + goto retry;
This looks strange why we need zap pte here?
> + }
> +
> +
> if (pte_file(entry))
> return do_nonlinear_fault(mm, vma, address,
> pte, pmd, flags, entry);
> diff --git a/mm/rmap.c b/mm/rmap.c
> index d9d4231..2b6f079 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -728,6 +728,11 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
> referenced++;
> }
> pte_unmap_unlock(pte, ptl);
> + if (vma->vm_flags & VM_VOLATILE) {
> + pra->mapcount = 0;
> + pra->vm_flags |= VM_VOLATILE;
> + return SWAP_FAIL;
> + }
> }
>
> if (referenced) {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a9c74b4..34f159a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -43,6 +43,7 @@
> #include <linux/sysctl.h>
> #include <linux/oom.h>
> #include <linux/prefetch.h>
> +#include <linux/vrange.h>
>
> #include <asm/tlbflush.h>
> #include <asm/div64.h>
> @@ -683,6 +684,7 @@ enum page_references {
> PAGEREF_RECLAIM,
> PAGEREF_RECLAIM_CLEAN,
> PAGEREF_KEEP,
> + PAGEREF_DISCARD,
"discard" is alread used in various place for another meanings.
another name is better.
> PAGEREF_ACTIVATE,
> };
>
> @@ -703,6 +705,13 @@ static enum page_references page_check_references(struct page *page,
> if (vm_flags & VM_LOCKED)
> return PAGEREF_RECLAIM;
>
> + /*
> + * If volatile page is reached on LRU's tail, we discard the
> + * page without considering recycle the page.
> + */
> + if (vm_flags & VM_VOLATILE)
> + return PAGEREF_DISCARD;
> +
> if (referenced_ptes) {
> if (PageSwapBacked(page))
> return PAGEREF_ACTIVATE;
> @@ -930,6 +939,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> switch (references) {
> case PAGEREF_ACTIVATE:
> goto activate_locked;
> + case PAGEREF_DISCARD:
> + if (may_enter_fs && !discard_vpage(page))
Wny may-enter-fs is needed? discard_vpage never enter FS.
> + goto free_it;
> case PAGEREF_KEEP:
> goto keep_locked;
> case PAGEREF_RECLAIM:
> diff --git a/mm/vrange.c b/mm/vrange.c
> index 1ff3cbd..28ceb6f 100644
> --- a/mm/vrange.c
> +++ b/mm/vrange.c
> @@ -246,3 +246,117 @@ SYSCALL_DEFINE5(vrange, unsigned long, start, size_t, len, unsigned long, mode,
> out:
> return ret;
> }
> +
> +
> +/**
> + * try_to_discard_one - Purge a volatile page from a vma
> + *
> + * Finds the pte for a page in a vma, marks the pte as purged
> + * and release the page.
> + */
> +static void try_to_discard_one(struct page *page, struct vm_area_struct *vma)
> +{
> + struct mm_struct *mm = vma->vm_mm;
> + pte_t *pte;
> + pte_t pteval;
> + spinlock_t *ptl;
> + unsigned long addr;
> +
> + VM_BUG_ON(!PageLocked(page));
> +
> + addr = vma_address(page, vma);
> + pte = page_check_address(page, mm, addr, &ptl, 0);
> + if (!pte)
> + return;
> +
> + BUG_ON(vma->vm_flags & (VM_SPECIAL|VM_LOCKED|VM_MIXEDMAP|VM_HUGETLB));
> +
> + flush_cache_page(vma, addr, page_to_pfn(page));
> + pteval = ptep_clear_flush(vma, addr, pte);
> +
> + update_hiwater_rss(mm);
> + if (PageAnon(page))
> + dec_mm_counter(mm, MM_ANONPAGES);
> + else
> + dec_mm_counter(mm, MM_FILEPAGES);
> +
> + page_remove_rmap(page);
> + page_cache_release(page);
> +
> + set_pte_at(mm, addr, pte,
> + swp_entry_to_pte(make_vpurged_entry()));
> +
> + pte_unmap_unlock(pte, ptl);
> + mmu_notifier_invalidate_page(mm, addr);
> +
> +}
> +
> +/**
> + * try_to_discard_vpage - check vma chain and discard from vmas marked volatile
> + *
> + * Goes over all the vmas that hold a page, and where the vmas are volatile,
> + * purge the page from the vma.
> + *
> + * Returns 0 on success, -1 on error.
> + */
> +static int try_to_discard_vpage(struct page *page)
> +{
> + struct anon_vma *anon_vma;
> + struct anon_vma_chain *avc;
> + pgoff_t pgoff;
> +
> + anon_vma = page_lock_anon_vma_read(page);
> + if (!anon_vma)
> + return -1;
> +
> + pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> + /*
> + * During interating the loop, some processes could see a page as
> + * purged while others could see a page as not-purged because we have
> + * no global lock between parent and child for protecting vrange system
> + * call during this loop. But it's not a problem because the page is
> + * not *SHARED* page but *COW* page so parent and child can see other
> + * data anytime. The worst case by this race is a page was purged
> + * but couldn't be discarded so it makes unnecessary page fault but
> + * it wouldn't be severe.
> + */
> + anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
> + struct vm_area_struct *vma = avc->vma;
> +
> + if (!(vma->vm_flags & VM_VOLATILE))
> + continue;
When you find !VM_VOLATILE vma, we have no reason to continue pte zapping.
Isn't it?
> + try_to_discard_one(page, vma);
> + }
> + page_unlock_anon_vma_read(anon_vma);
> + return 0;
> +}
> +
> +
> +/**
> + * discard_vpage - If possible, discard the specified volatile page
> + *
> + * Attempts to discard a volatile page, and if needed frees the swap page
> + *
> + * Returns 0 on success, -1 on error.
> + */
> +int discard_vpage(struct page *page)
> +{
> + VM_BUG_ON(!PageLocked(page));
> + VM_BUG_ON(PageLRU(page));
> +
> + /* XXX - for now we only support anonymous volatile pages */
> + if (!PageAnon(page))
> + return -1;
> +
> + if (!try_to_discard_vpage(page)) {
> + if (PageSwapCache(page))
> + try_to_free_swap(page);
This looks strange. try_to_free_swap can't handle vpurge pseudo entry.
> +
> + if (page_freeze_refs(page, 1)) {
Where is page_unfreeze_refs() for the pair of this?
> + unlock_page(page);
> + return 0;
> + }
> + }
> +
> + return -1;
> +}
> --
> 1.8.3.2
>
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