Messages in this thread | | | Date | Tue, 03 Apr 2007 17:15:45 -0400 | From | Rik van Riel <> | Subject | Re: missing madvise functionality |
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Eric Dumazet wrote: > Rik van Riel a écrit : >> Andrew Morton wrote: >> >>> Oh. I was assuming that we'd want to unmap these pages from >>> pagetables and >>> mark then super-easily-reclaimable. So a later touch would incur a >>> minor >>> fault. >>> >>> But you think that we should leave them mapped into pagetables so no >>> such >>> fault occurs. >> >>> Leaving the pages mapped into pagetables means that they are >>> considerably >>> less likely to be reclaimed. >> >> If we move the pages to a place where they are very likely to be >> reclaimed quickly (end of the inactive list, or a separate >> reclaim list) and clear the dirty and referenced lists, we can >> both reclaim the page easily *and* avoid the page fault penalty. >> > > There is one possible speedup : > > - If an user app does a madvise(MADV_DONTNEED), we can assume the pages > can later be bring back without need to zero them. The application > doesnt care.
... however, the application that previously used that page might care a lot!
> mmap()/brk() must give fresh NULL pages, but maybe > madvise(MADV_DONTNEED) can relax this requirement (if the pages were > reclaimed, then a page fault could bring a new page with random content)
If we bring in a new page, it has to be zeroed for security reasons.
You don't want somebody else's process to get a page with your password in it.
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