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Message-ID: <2110609.1zlQqR5hOE@nvdebian>
Date: Tue, 2 Mar 2021 19:52:53 +1100
From: Alistair Popple <apopple@...dia.com>
To: Christoph Hellwig <hch@...radead.org>
CC: <linux-mm@...ck.org>, <nouveau@...ts.freedesktop.org>,
<bskeggs@...hat.com>, <akpm@...ux-foundation.org>,
<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<dri-devel@...ts.freedesktop.org>, <jhubbard@...dia.com>,
<rcampbell@...dia.com>, <jglisse@...hat.com>, <jgg@...dia.com>,
<daniel@...ll.ch>
Subject: Re: [PATCH v3 1/8] mm: Remove special swap entry functions
On Saturday, 27 February 2021 2:59:09 AM AEDT Christoph Hellwig wrote:
> > - struct page *page = migration_entry_to_page(entry);
> > + struct page *page = pfn_to_page(swp_offset(entry));
>
> I wonder if keeping a single special_entry_to_page() helper would still
> me a useful. But I'm not entirely sure. There are also two more open
> coded copies of this in the THP migration code.
I think it might be if only to clearly document where these entries are used.
Will add it for the next version to see what it looks like.
> > -#define free_swap_and_cache(e) ({(is_migration_entry(e) ||
is_device_private_entry(e));})
> > -#define swapcache_prepare(e) ({(is_migration_entry(e) ||
is_device_private_entry(e));})
> > +#define free_swap_and_cache(e) is_special_entry(e)
> > +#define swapcache_prepare(e) is_special_entry(e)
>
> Staring at this I'm really, really confused at what this is doing.
>
> Looking a little closer these are the !CONFIG_SWAP stubs, but it could
> probably use a comment or two.
Will do, thanks.
- Alistair
> > } else if (is_migration_entry(entry)) {
> > - page = migration_entry_to_page(entry);
> > + page = pfn_to_page(swp_offset(entry));
> >
> > rss[mm_counter(page)]++;
> >
> > @@ -737,7 +737,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct
mm_struct *src_mm,
> > set_pte_at(src_mm, addr, src_pte, pte);
> > }
> > } else if (is_device_private_entry(entry)) {
> > - page = device_private_entry_to_page(entry);
> > + page = pfn_to_page(swp_offset(entry));
> >
> > /*
> > * Update rss count even for unaddressable pages, as
> > @@ -1274,7 +1274,7 @@ static unsigned long zap_pte_range(struct mmu_gather
*tlb,
> >
> > entry = pte_to_swp_entry(ptent);
> > if (is_device_private_entry(entry)) {
> > - struct page *page = device_private_entry_to_page(entry);
> > + struct page *page = pfn_to_page(swp_offset(entry));
> >
> > if (unlikely(details && details->check_mapping)) {
> > /*
> > @@ -1303,7 +1303,7 @@ static unsigned long zap_pte_range(struct mmu_gather
*tlb,
> > else if (is_migration_entry(entry)) {
> > struct page *page;
> >
> > - page = migration_entry_to_page(entry);
> > + page = pfn_to_page(swp_offset(entry));
> > rss[mm_counter(page)]--;
> > }
> > if (unlikely(!free_swap_and_cache(entry)))
> > @@ -3271,7 +3271,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> > migration_entry_wait(vma->vm_mm, vmf->pmd,
> > vmf->address);
> > } else if (is_device_private_entry(entry)) {
> > - vmf->page = device_private_entry_to_page(entry);
> > + vmf->page = pfn_to_page(swp_offset(entry));
> > ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
> > } else if (is_hwpoison_entry(entry)) {
> > ret = VM_FAULT_HWPOISON;
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 20ca887ea769..72adcc3d8f5b 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -321,7 +321,7 @@ void __migration_entry_wait(struct mm_struct *mm,
pte_t *ptep,
> > if (!is_migration_entry(entry))
> > goto out;
> >
> > - page = migration_entry_to_page(entry);
> > + page = pfn_to_page(swp_offset(entry));
> >
> > /*
> > * Once page cache replacement of page migration started, page_count
> > @@ -361,7 +361,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm,
pmd_t *pmd)
> > ptl = pmd_lock(mm, pmd);
> > if (!is_pmd_migration_entry(*pmd))
> > goto unlock;
> > - page = migration_entry_to_page(pmd_to_swp_entry(*pmd));
> > + page = pfn_to_page(swp_offset(pmd_to_swp_entry(*pmd)));
> > if (!get_page_unless_zero(page))
> > goto unlock;
> > spin_unlock(ptl);
> > @@ -2437,7 +2437,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> > if (!is_device_private_entry(entry))
> > goto next;
> >
> > - page = device_private_entry_to_page(entry);
> > + page = pfn_to_page(swp_offset(entry));
> > if (!(migrate->flags &
> > MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
> > page->pgmap->owner != migrate->pgmap_owner)
> > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> > index 86e3a3688d59..34230d08556a 100644
> > --- a/mm/page_vma_mapped.c
> > +++ b/mm/page_vma_mapped.c
> > @@ -96,7 +96,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
> > if (!is_migration_entry(entry))
> > return false;
> >
> > - pfn = migration_entry_to_pfn(entry);
> > + pfn = swp_offset(entry);
> > } else if (is_swap_pte(*pvmw->pte)) {
> > swp_entry_t entry;
> >
> > @@ -105,7 +105,7 @@ static bool check_pte(struct page_vma_mapped_walk
*pvmw)
> > if (!is_device_private_entry(entry))
> > return false;
> >
> > - pfn = device_private_entry_to_pfn(entry);
> > + pfn = swp_offset(entry);
> > } else {
> > if (!pte_present(*pvmw->pte))
> > return false;
> > @@ -200,7 +200,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk
*pvmw)
> > if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
> > swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
> >
> > - if (migration_entry_to_page(entry) != page)
> > + if (pfn_to_page(swp_offset(entry)) != page)
> > return not_found(pvmw);
> > return true;
> > }
> ---end quoted text---
>
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