1. 23 6月, 2008 38 次提交
  2. 21 6月, 2008 1 次提交
    • L
      Reinstate ZERO_PAGE optimization in 'get_user_pages()' and fix XIP · 89f5b7da
      Linus Torvalds 提交于
      KAMEZAWA Hiroyuki and Oleg Nesterov point out that since the commit
      557ed1fa ("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: NOleg Nesterov <oleg@tv-sign.ru>
      Acked-by: NNick 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: NLinus Torvalds <torvalds@linux-foundation.org>
      89f5b7da
  3. 19 6月, 2008 1 次提交