From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 59C2D5F0001 for ; Fri, 17 Apr 2009 03:02:14 -0400 (EDT) Received: by rv-out-0708.google.com with SMTP id f25so613253rvb.26 for ; Fri, 17 Apr 2009 00:02:15 -0700 (PDT) Message-ID: <49E8292D.7050904@gmail.com> Date: Fri, 17 Apr 2009 15:01:01 +0800 From: Huang Shijie MIME-Version: 1.0 Subject: Does get_user_pages_fast lock the user pages in memory in my case? Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: linux-mm@kvack.org List-ID: I'm writting a driver for a video card with the V4L2 interface . V4L2 interface supports the USER-POINTER method for the video frame handling. VLC player supports the USER-POINTER method,while MPALYER does not. In the USER-POINTER method, VLC will call the posix_memalign() to allocate 203 pages in certain PAL mode (that is 720*576*2) for a single frame. In my driver , I call the get_user_pages_fast() to obtain the pages array,and then call the vmap() to map the pages to VMALLOC space for the memcpy().The code shows below: .................... get_user_pages_fast(); ... f->data = vmap(); ....................... In comments, it said : " +/** + * get_user_pages_fast() - pin user pages in memory + * @start: starting user address + * @nr_pages: number of pages from start to pin + * @write: whether pages will be written to + * @pages: array that receives pointers to the pages pinned. + * Should be at least nr_pages long. " But after I digged the code of kswap and the get_user_pages(called by get_user_pages_fast), I did not find how the pages pinned in memory.I really need the pages pinned in memory. Assume page A is one of the pages obtained by get_user_pages_fast() during page-fault. [1] page A will on the LRU_ACTIVE_ANON list; the _count of page A increment by one; PTE for page A will be set ACCESSED. [2] kswapd will scan the lru list,and move page A from LRU_ACTIVE_ANON to LRU_INACTIVE_ANON. In the shrink_page_list(), there is nothing can stop page A been swapped out. I don't think the page_reference() can move page A back to LRU_ACTIVE_ANON.In my driver, I am not sure if the VLC can access the page A. Is this a bug? or I miss something? Thanks . -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org