Reinstate ZERO_PAGE optimization in 'get_user_pages()' and fix XIP
KAMEZAWA Hiroyuki and Oleg Nesterov point out that since the commit
557ed1fa26
("remove ZERO_PAGE") removed
the ZERO_PAGE from the VM mappings, any users of get_user_pages() will
generally now populate the VM with real empty pages needlessly.
We used to get the ZERO_PAGE when we did the "handle_mm_fault()", but
since fault handling no longer uses ZERO_PAGE for new anonymous pages,
we now need to handle that special case in follow_page() instead.
In particular, the removal of ZERO_PAGE effectively removed the core
file writing optimization where we would skip writing pages that had not
been populated at all, and increased memory pressure a lot by allocating
all those useless newly zeroed pages.
This reinstates the optimization by making the unmapped PTE case the
same as for a non-existent page table, which already did this correctly.
While at it, this also fixes the XIP case for follow_page(), where the
caller could not differentiate between the case of a page that simply
could not be used (because it had no "struct page" associated with it)
and a page that just wasn't mapped.
We do that by simply returning an error pointer for pages that could not
be turned into a "struct page *". The error is arbitrarily picked to be
EFAULT, since that was what get_user_pages() already used for the
equivalent IO-mapped page case.
[ Also removed an impossible test for pte_offset_map_lock() failing:
that's not how that function works ]
Acked-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Родитель
9bedbcb207
Коммит
89f5b7da2a
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@ -142,7 +142,7 @@ static void dump_one_vdso_page(struct page *pg, struct page *upg)
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printk("kpg: %p (c:%d,f:%08lx)", __va(page_to_pfn(pg) << PAGE_SHIFT),
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page_count(pg),
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pg->flags);
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if (upg/* && pg != upg*/) {
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if (upg && !IS_ERR(upg) /* && pg != upg*/) {
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printk(" upg: %p (c:%d,f:%08lx)", __va(page_to_pfn(upg)
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<< PAGE_SHIFT),
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page_count(upg),
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17
mm/memory.c
17
mm/memory.c
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@ -999,17 +999,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
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goto no_page_table;
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ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
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if (!ptep)
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goto out;
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pte = *ptep;
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if (!pte_present(pte))
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goto unlock;
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goto no_page;
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if ((flags & FOLL_WRITE) && !pte_write(pte))
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goto unlock;
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page = vm_normal_page(vma, address, pte);
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if (unlikely(!page))
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goto unlock;
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goto bad_page;
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if (flags & FOLL_GET)
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get_page(page);
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@ -1024,6 +1022,15 @@ unlock:
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out:
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return page;
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bad_page:
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pte_unmap_unlock(ptep, ptl);
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return ERR_PTR(-EFAULT);
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no_page:
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pte_unmap_unlock(ptep, ptl);
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if (!pte_none(pte))
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return page;
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/* Fall through to ZERO_PAGE handling */
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no_page_table:
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/*
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* When core dumping an enormous anonymous area that nobody
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@ -1159,6 +1166,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
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cond_resched();
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}
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if (IS_ERR(page))
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return i ? i : PTR_ERR(page);
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if (pages) {
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pages[i] = page;
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10
mm/migrate.c
10
mm/migrate.c
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@ -865,6 +865,11 @@ static int do_move_pages(struct mm_struct *mm, struct page_to_node *pm,
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goto set_status;
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page = follow_page(vma, pp->addr, FOLL_GET);
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err = PTR_ERR(page);
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if (IS_ERR(page))
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goto set_status;
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err = -ENOENT;
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if (!page)
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goto set_status;
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@ -928,6 +933,11 @@ static int do_pages_stat(struct mm_struct *mm, struct page_to_node *pm)
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goto set_status;
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page = follow_page(vma, pm->addr, 0);
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err = PTR_ERR(page);
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if (IS_ERR(page))
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goto set_status;
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err = -ENOENT;
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/* Use PageReserved to check for zero page */
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if (!page || PageReserved(page))
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