Messages in this thread | | | Date | Thu, 28 Apr 2011 11:29:01 +0200 | From | Andrea Righi <> | Subject | Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED_FS |
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On Wed, Apr 27, 2011 at 12:33:08PM -0600, Matthew Wilcox wrote: > On Wed, Apr 27, 2011 at 08:13:47PM +0200, Andrea Righi wrote: > > @@ -127,6 +128,12 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) > > invalidate_mapping_pages(mapping, start_index, > > end_index); > > break; > > + case POSIX_FADV_DONTNEED_FS: > > + if (capable(CAP_SYS_ADMIN)) > > + drop_pagecache_sb(file->f_dentry->d_sb, NULL); > > + else > > + ret = -EPERM; > > + break; > > default: > > ret = -EINVAL; > > } > > Mmm ... what if I open /dev/sdxyz and call fadvise() on it? I think > you end up flushing /dev's page cache entries, instead of the filesystem > which is on /dev/sdxyz. > > If I understand correctly, you want mapping->host->i_sb instead of > file->f_dentry->d_sb.
I did some tests, but I don't get the expected behaviour. In all cases both if I use mapping->host->i_sb or file->f_dentry->d_sb when I call fadvise() on any block device all the blockdev pages are dropped ("Buffers" from /proc/meminfo), but page cache pages are not touched:
# df -hT / Filesystem Type Size Used Avail Use% Mounted on /dev/sda1 ext4 29G 20G 7.4G 73% / # grep "^Cached\|Buffers" /proc/meminfo Buffers: 79772 kB Cached: 32440 kB # sudo drop-pagecache /dev/sda1 # grep "^Cached\|Buffers" /proc/meminfo Buffers: 228 kB Cached: 32440 kB # sudo drop-pagecache / # grep "^Cached\|Buffers" /proc/meminfo Buffers: 228 kB Cached: 4884 kB
Thanks, -Andrea
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