在 2020/7/3 6:56, Song Liu 写道:
On Thu, Jul 2, 2020 at 5:05 AM Yufen Yu <yuyufen@xxxxxxxxxx> wrote:Since grow_buffers() uses alloc_page() to allocate the buffers for each stripe_head(), means, it will allocate 64K buffers and just use 4K of them, after setting stripe_size as 4096. To avoid wasting memory, we try to contain multiple 'page' of sh->dev into one real page. That means, multiple sh->dev[i].page will point to the only page with different offset. Example of 64K PAGE_SIZE and 4K stripe_size as following: 64K PAGE_SIZE +---+---+---+---+------------------------------+ | | | | | | | | | | +-+-+-+-+-+-+-+-+------------------------------+ ^ ^ ^ ^ | | | +----------------------------+ | | | | | | +-------------------+ | | | | | | +----------+ | | | | | | +-+ | | | | | | | +-----+-----+------+-----+------+-----+------+------+ sh | offset(0) | offset(4K) | offset(8K) | offset(12K) | + +-----------+------------+------------+-------------+ +----> dev[0].page dev[1].page dev[2].page dev[3].page After trying to share one page, the users of sh->dev[i].page need to take care: 1) When issue bio into stripe_head, bi_io_vec.bv_page will point to the page directly. So, we should make sure bv_offset to been set with correct offset. 2) When compute xor, the page will be passed to computer function. So, we also need to pass offset of that page to computer. Let it compute correct location of each sh->dev[i].page. This patch will add a new member of r5pages into stripe_head to manage all pages needed by each sh->dev[i]. We also add 'offset' for each r5dev so that users can get related page offset easily. And add helper function to get page and it's index in r5pages array by disk index. Signed-off-by: Yufen Yu <yuyufen@xxxxxxxxxx> --- drivers/md/raid5.h | 61 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+)
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+/* + * Return corresponding page index of r5pages array. + */ +static inline int raid5_get_page_index(struct stripe_head *sh, int disk_idx) +{ + struct r5conf *conf = sh->raid_conf; + int cnt; + + WARN_ON(!sh->pages.page); + BUG_ON(conf->stripe_size > PAGE_SIZE);We have too many of these WARN_ON() and BUG_ON().
Yes. Yufen, please avoid using BUG_ON() becuase we are reducing the usage of it and Linus hate it:
https://lkml.org/lkml/2013/5/17/254 https://linuxinsider.com/story/torvalds-blows-stack-over-buggy-new-kernel-83975.html https://lore.kernel.org/patchwork/patch/568291/ Thanks, Jason
