On Mon, 9 Sep 2002, Haijin Yan wrote: > Are you guys saying that pages for traditional I/O(read/write) do not > have page->mapping while clean mmap()ed pages do not have page->buffer? No. Any pagecache page has page->mapping and page->index, no matter whether it's used for read/write or for mmap. These pages will have page->buffers when we're doing _disk_ IO on them, buffer heads are the way the kernel tells the block IO subsystem what should be done with a page. > so when is the condition (!page->mapping) true and what it represents for? It can happen in 3 situations: 1) a new anonymous page is allocated to the process, this is a private page that is only visible in the process page tables 2) a page _was_ part of a page cache mapping, but truncate() removed it from the page cache ... at the same time, a process was doing a pagefault on this page and added it to its page tables, now the page is converted into anonymous memory 3) a page was swapped in and removed from the swap cache in order to reclaim swap space. > If page->buffers is true, Does that ony mean either page is brought in > by traditional IO or a disk block is allocated for this mmap()ed page > for written(because page is dirty)? Yes, but note that buffer heads can stay around after disk IO has finished. regards, Rik -- Spamtrap of the month: september@surriel.com http://www.surriel.com/ http://distro.conectiva.com/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
