• Hugh Dickins's avatar
    [PATCH] freepgt: free_pgtables use vma list · e0da382c
    Hugh Dickins authored
    Recent woes with some arches needing their own pgd_addr_end macro; and 4-level
    clear_page_range regression since 2.6.10's clear_page_tables; and its
    long-standing well-known inefficiency in searching throughout the higher-level
    page tables for those few entries to clear and free: all can be blamed on
    ignoring the list of vmas when we free page tables.
    
    Replace exit_mmap's clear_page_range of the total user address space by
    free_pgtables operating on the mm's vma list; unmap_region use it in the same
    way, giving floor and ceiling beyond which it may not free tables.  This
    brings lmbench fork/exec/sh numbers back to 2.6.10 (unless preempt is enabled,
    in which case latency fixes spoil unmap_vmas throughput).
    
    Beware: the do_mmap_pgoff driver failure case must now use unmap_region
    instead of zap_page_range, since a page table might have been allocated, and
    can only be freed while it is touched by some vma.
    
    Move free_pgtables from mmap.c to memory.c, where its lower levels are adapted
    from the clear_page_range levels.  (Most of free_pgtables' old code was
    actually for a non-existent case, prev not properly set up, dating from before
    hch gave us split_vma.) Pass mmu_gather** in the public interfaces, since we
    might want to add latency lockdrops later; but no attempt to do so yet, going
    by vma should itself reduce latency.
    
    But what if is_hugepage_only_range?  Those ia64 and ppc64 cases need careful
    examination: put that off until a later patch of the series.
    
    What of x86_64's 32bit vdso page __map_syscall32 maps outside any vma?
    
    And the range to sparc64's flush_tlb_pgtables?  It's less clear to me now that
    we need to do more than is done here - every PMD_SIZE ever occupied will be
    flushed, do we really have to flush every PGDIR_SIZE ever partially occupied? 
    A shame to complicate it unnecessarily.
    
    Special thanks to David Miller for time spent repairing my ceilings.
    Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    e0da382c
pgtable.c 6.39 KB