From c4b4c2a78a9fc0c532c58504e8cb5441224ff1d9 Mon Sep 17 00:00:00 2001 From: Zhiqiang Liu Date: Mon, 13 Apr 2020 13:12:10 +0800 Subject: buffer: remove useless comment and WB_REASON_FREE_MORE_MEM, reason. free_more_memory func has been completely removed in commit bc48f001de12 ("buffer: eliminate the need to call free_more_memory() in __getblk_slow()") So comment and `WB_REASON_FREE_MORE_MEM` reason about free_more_memory are no longer needed. Fixes: bc48f001de12 ("buffer: eliminate the need to call free_more_memory() in __getblk_slow()") Reviewed-by: Jan Kara Signed-off-by: Zhiqiang Liu Signed-off-by: Jens Axboe --- fs/buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/buffer.c b/fs/buffer.c index f73276d746bb..763de99508de 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -967,7 +967,7 @@ grow_dev_page(struct block_device *bdev, sector_t block, struct page *page; struct buffer_head *bh; sector_t end_block; - int ret = 0; /* Will call free_more_memory() */ + int ret = 0; gfp_t gfp_mask; gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp; -- cgit v1.2.3 From b849dd84b6ccfe32622988b79b7b073861fcf9f7 Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Tue, 24 Mar 2020 14:48:27 -0700 Subject: bdev: Reduce time holding bd_mutex in sync in blkdev_close() While trying to "dd" to the block device for a USB stick, I encountered a hung task warning (blocked for > 120 seconds). I managed to come up with an easy way to reproduce this on my system (where /dev/sdb is the block device for my USB stick) with: while true; do dd if=/dev/zero of=/dev/sdb bs=4M; done With my reproduction here are the relevant bits from the hung task detector: INFO: task udevd:294 blocked for more than 122 seconds. ... udevd D 0 294 1 0x00400008 Call trace: ... mutex_lock_nested+0x40/0x50 __blkdev_get+0x7c/0x3d4 blkdev_get+0x118/0x138 blkdev_open+0x94/0xa8 do_dentry_open+0x268/0x3a0 vfs_open+0x34/0x40 path_openat+0x39c/0xdf4 do_filp_open+0x90/0x10c do_sys_open+0x150/0x3c8 ... ... Showing all locks held in the system: ... 1 lock held by dd/2798: #0: ffffff814ac1a3b8 (&bdev->bd_mutex){+.+.}, at: __blkdev_put+0x50/0x204 ... dd D 0 2798 2764 0x00400208 Call trace: ... schedule+0x8c/0xbc io_schedule+0x1c/0x40 wait_on_page_bit_common+0x238/0x338 __lock_page+0x5c/0x68 write_cache_pages+0x194/0x500 generic_writepages+0x64/0xa4 blkdev_writepages+0x24/0x30 do_writepages+0x48/0xa8 __filemap_fdatawrite_range+0xac/0xd8 filemap_write_and_wait+0x30/0x84 __blkdev_put+0x88/0x204 blkdev_put+0xc4/0xe4 blkdev_close+0x28/0x38 __fput+0xe0/0x238 ____fput+0x1c/0x28 task_work_run+0xb0/0xe4 do_notify_resume+0xfc0/0x14bc work_pending+0x8/0x14 The problem appears related to the fact that my USB disk is terribly slow and that I have a lot of RAM in my system to cache things. Specifically my writes seem to be happening at ~15 MB/s and I've got ~4 GB of RAM in my system that can be used for buffering. To write 4 GB of buffer to disk thus takes ~4000 MB / ~15 MB/s = ~267 seconds. The 267 second number is a problem because in __blkdev_put() we call sync_blockdev() while holding the bd_mutex. Any other callers who want the bd_mutex will be blocked for the whole time. The problem is made worse because I believe blkdev_put() specifically tells other tasks (namely udev) to go try to access the device at right around the same time we're going to hold the mutex for a long time. Putting some traces around this (after disabling the hung task detector), I could confirm: dd: 437.608600: __blkdev_put() right before sync_blockdev() for sdb udevd: 437.623901: blkdev_open() right before blkdev_get() for sdb dd: 661.468451: __blkdev_put() right after sync_blockdev() for sdb udevd: 663.820426: blkdev_open() right after blkdev_get() for sdb A simple fix for this is to realize that sync_blockdev() works fine if you're not holding the mutex. Also, it's not the end of the world if you sync a little early (though it can have performance impacts). Thus we can make a guess that we're going to need to do the sync and then do it without holding the mutex. We still do one last sync with the mutex but it should be much, much faster. With this, my hung task warnings for my test case are gone. Signed-off-by: Douglas Anderson Reviewed-by: Guenter Roeck Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/block_dev.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'fs') diff --git a/fs/block_dev.c b/fs/block_dev.c index 52b6f646cdbd..59435f07911a 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1893,6 +1893,16 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part) struct gendisk *disk = bdev->bd_disk; struct block_device *victim = NULL; + /* + * Sync early if it looks like we're the last one. If someone else + * opens the block device between now and the decrement of bd_openers + * then we did a sync that we didn't need to, but that's not the end + * of the world and we want to avoid long (could be several minute) + * syncs while holding the mutex. + */ + if (bdev->bd_openers == 1) + sync_blockdev(bdev); + mutex_lock_nested(&bdev->bd_mutex, for_part); if (for_part) bdev->bd_part_count--; -- cgit v1.2.3 From d56deb1e4e6696b2c70815beb8d1d39fc0063b1c Mon Sep 17 00:00:00 2001 From: "Ma, Jianpeng" Date: Tue, 21 Apr 2020 11:48:08 +0000 Subject: block: remove unused header Dax related code already removed from this file. Reviewed-by: Christoph Hellwig Signed-off-by: Jianpeng Ma Signed-off-by: Jens Axboe --- fs/block_dev.c | 1 - 1 file changed, 1 deletion(-) (limited to 'fs') diff --git a/fs/block_dev.c b/fs/block_dev.c index 59435f07911a..93672c3f1c78 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -19,7 +19,6 @@ #include #include #include -#include #include #include #include -- cgit v1.2.3