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Message-ID: <CAOUHufZBoV-ujMF3v60Sj4bARb5vRg7cpcRsqTiKHB4CKZc_fw@mail.gmail.com>
Date: Thu, 13 Jul 2023 21:57:29 -0600
From: Yu Zhao <yuzhao@...gle.com>
To: Yin Fengwei <fengwei.yin@...el.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, willy@...radead.org, david@...hat.com,
ryan.roberts@....com, shy828301@...il.com
Subject: Re: [RFC PATCH] madvise: make madvise_cold_or_pageout_pte_range()
support large folio
On Thu, Jul 13, 2023 at 9:06 AM Yin Fengwei <fengwei.yin@...el.com> wrote:
>
> Current madvise_cold_or_pageout_pte_range() has two problems for
> large folio support:
> - Using folio_mapcount() with large folio prevent large folio from
> picking up.
> - If large folio is in the range requested, shouldn't split it
> in madvise_cold_or_pageout_pte_range().
>
> Fix them by:
> - Use folio_estimated_sharers() with large folio
> - If large folio is in the range requested, don't split it. Leave
> to page reclaim phase.
>
> For large folio cross boundaries of requested range, skip it if it's
> page cache. Try to split it if it's anonymous folio. If splitting
> fails, skip it.
>
> The main reason to call folio_referenced() is to clear the yong of
> conresponding PTEs. So in page reclaim phase, there is good chance
> the folio can be reclaimed.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@...el.com>
> ---
> This patch is based on mlock large folio support rfc2 as it depends
> on the folio_in_range() added by that patchset
>
> Also folio_op_size() can be unitfied with get_folio_mlock_step().
>
> Testing done:
> - kselftest: No new regression introduced.
>
> mm/madvise.c | 133 ++++++++++++++++++++++++++++++++-------------------
> 1 file changed, 84 insertions(+), 49 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 38382a5d1e393..5748cf098235d 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -31,6 +31,7 @@
> #include <linux/swapops.h>
> #include <linux/shmem_fs.h>
> #include <linux/mmu_notifier.h>
> +#include <linux/kernel.h>
>
> #include <asm/tlb.h>
>
> @@ -339,6 +340,35 @@ static inline bool can_do_file_pageout(struct vm_area_struct *vma)
> file_permission(vma->vm_file, MAY_WRITE) == 0;
> }
>
> +static inline bool skip_current_entry(struct folio *folio, bool pageout_anon)
> +{
> + if (!folio)
> + return true;
> +
> + if (folio_is_zone_device(folio))
> + return true;
> +
> + if (!folio_test_lru(folio))
> + return true;
> +
> + if (pageout_anon && !folio_test_anon(folio))
> + return true;
> +
> + if (folio_test_unevictable(folio))
> + return true;
> +
> + return false;
> +}
> +
> +static inline unsigned int folio_op_size(struct folio *folio, pte_t pte,
> + unsigned long addr, unsigned long end)
> +{
> + unsigned int nr;
> +
> + nr = folio_pfn(folio) + folio_nr_pages(folio) - pte_pfn(pte);
> + return min_t(unsigned int, nr, (end - addr) >> PAGE_SHIFT);
> +}
> +
> static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> unsigned long addr, unsigned long end,
> struct mm_walk *walk)
> @@ -353,6 +383,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> struct folio *folio = NULL;
> LIST_HEAD(folio_list);
> bool pageout_anon_only_filter;
> + unsigned long start = addr;
>
> if (fatal_signal_pending(current))
> return -EINTR;
> @@ -383,7 +414,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> folio = pfn_folio(pmd_pfn(orig_pmd));
>
> /* Do not interfere with other mappings of this folio */
> - if (folio_mapcount(folio) != 1)
> + if (folio_estimated_sharers(folio) != 1)
> goto huge_unlock;
>
> if (pageout_anon_only_filter && !folio_test_anon(folio))
> @@ -442,78 +473,60 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> for (; addr < end; pte++, addr += PAGE_SIZE) {
> ptent = ptep_get(pte);
>
> - if (pte_none(ptent))
> - continue;
> -
> - if (!pte_present(ptent))
> + if (pte_none(ptent) || !pte_present(ptent))
> continue;
>
> folio = vm_normal_folio(vma, addr, ptent);
> - if (!folio || folio_is_zone_device(folio))
> + if (skip_current_entry(folio, pageout_anon_only_filter))
> continue;
>
> /*
> - * Creating a THP page is expensive so split it only if we
> - * are sure it's worth. Split it if we are only owner.
> + * Split large folio if it's anonymous and cross the
> + * boundaries of request range.
> */
> if (folio_test_large(folio)) {
> - int err;
> + int err, step;
> +
> + if (folio_estimated_sharers(folio) != 1)
> + continue;
> +
> + if (folio_in_range(folio, vma, start, end))
> + goto pageout_cold_folio;
>
> - if (folio_mapcount(folio) != 1)
> - break;
> - if (pageout_anon_only_filter && !folio_test_anon(folio))
> - break;
> - if (!folio_trylock(folio))
> - break;
> folio_get(folio);
> + step = folio_op_size(folio, ptent, addr, end);
> + if (!folio_test_anon(folio) || !folio_trylock(folio)) {
> + folio_put(folio);
> + goto next_folio;
> + }
> +
> arch_leave_lazy_mmu_mode();
> pte_unmap_unlock(start_pte, ptl);
> start_pte = NULL;
> err = split_folio(folio);
> folio_unlock(folio);
> folio_put(folio);
> - if (err)
> - break;
> +
> start_pte = pte =
> pte_offset_map_lock(mm, pmd, addr, &ptl);
> if (!start_pte)
> break;
> arch_enter_lazy_mmu_mode();
> - pte--;
> - addr -= PAGE_SIZE;
> - continue;
> - }
>
> - /*
> - * Do not interfere with other mappings of this folio and
> - * non-LRU folio.
> - */
> - if (!folio_test_lru(folio) || folio_mapcount(folio) != 1)
> + /* Skip the folio if split fails */
> + if (!err)
> + step = 0;
> +next_folio:
> + pte += step - 1;
> + addr += (step - 1) << PAGE_SHIFT;
> continue;
> + }
>
> - if (pageout_anon_only_filter && !folio_test_anon(folio))
> + /* Do not interfere with other mappings of this folio */
> + if (folio_mapcount(folio) != 1)
> continue;
>
> - VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
> -
> - if (pte_young(ptent)) {
> - ptent = ptep_get_and_clear_full(mm, addr, pte,
> - tlb->fullmm);
> - ptent = pte_mkold(ptent);
> - set_pte_at(mm, addr, pte, ptent);
> - tlb_remove_tlb_entry(tlb, pte, addr);
> - }
> -
> - /*
> - * We are deactivating a folio for accelerating reclaiming.
> - * VM couldn't reclaim the folio unless we clear PG_young.
> - * As a side effect, it makes confuse idle-page tracking
> - * because they will miss recent referenced history.
> - */
> - folio_clear_referenced(folio);
> - folio_test_clear_young(folio);
> - if (folio_test_active(folio))
> - folio_set_workingset(folio);
> +pageout_cold_folio:
> if (pageout) {
> if (folio_isolate_lru(folio)) {
> if (folio_test_unevictable(folio))
> @@ -529,8 +542,30 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> arch_leave_lazy_mmu_mode();
> pte_unmap_unlock(start_pte, ptl);
> }
> - if (pageout)
> - reclaim_pages(&folio_list);
> +
> + if (pageout) {
> + LIST_HEAD(reclaim_list);
> +
> + while (!list_empty(&folio_list)) {
> + int refs;
> + unsigned long flags;
> + struct mem_cgroup *memcg = folio_memcg(folio);
> +
> + folio = lru_to_folio(&folio_list);
> + list_del(&folio->lru);
> +
> + refs = folio_referenced(folio, 0, memcg, &flags);
> +
> + if ((flags & VM_LOCKED) || (refs == -1)) {
> + folio_putback_lru(folio);
> + continue;
> + }
> +
> + folio_test_clear_referenced(folio);
> + list_add(&folio->lru, &reclaim_list);
> + }
> + reclaim_pages(&reclaim_list);
> + }
i overlooked the chunk above -- it's unnecessary: after we split the
large folio (and splice the base folios onto the same LRU list), we
continue at the position of the first base folio because of:
pte--;
addr -= PAGE_SIZE;
continue;
And then we do pte_mkold(), which takes care of the A-bit.
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