Re: btrfs: why default 4M readahead size?

2010-03-19 Thread Jens Axboe
On Fri, Mar 19 2010, Shaohua Li wrote: > On Fri, Mar 19, 2010 at 04:22:11PM +0800, Jens Axboe wrote: > > On Fri, Mar 19 2010, Shaohua Li wrote: > > > On Fri, Mar 19, 2010 at 08:59:48AM +0800, Shaohua Li wrote: > > > > On Thu, Mar 18, 2010 at 08:53:13PM +0800, Chris Mason wrote: > > > > > On Thu, Ma

Re: btrfs: why default 4M readahead size?

2010-03-19 Thread Shaohua Li
On Fri, Mar 19, 2010 at 04:22:11PM +0800, Jens Axboe wrote: > On Fri, Mar 19 2010, Shaohua Li wrote: > > On Fri, Mar 19, 2010 at 08:59:48AM +0800, Shaohua Li wrote: > > > On Thu, Mar 18, 2010 at 08:53:13PM +0800, Chris Mason wrote: > > > > On Thu, Mar 18, 2010 at 09:42:57AM +0800, Shaohua Li wrote:

Re: btrfs: why default 4M readahead size?

2010-03-19 Thread Jens Axboe
On Fri, Mar 19 2010, Shaohua Li wrote: > On Fri, Mar 19, 2010 at 08:59:48AM +0800, Shaohua Li wrote: > > On Thu, Mar 18, 2010 at 08:53:13PM +0800, Chris Mason wrote: > > > On Thu, Mar 18, 2010 at 09:42:57AM +0800, Shaohua Li wrote: > > > > Btrfs uses below equation to calculate ra_pages: > > > >

Re: btrfs: why default 4M readahead size?

2010-03-18 Thread Shaohua Li
On Fri, Mar 19, 2010 at 08:59:48AM +0800, Shaohua Li wrote: > On Thu, Mar 18, 2010 at 08:53:13PM +0800, Chris Mason wrote: > > On Thu, Mar 18, 2010 at 09:42:57AM +0800, Shaohua Li wrote: > > > Btrfs uses below equation to calculate ra_pages: > > > fs_info->bdi.ra_pages = max(fs_info->bdi.ra_pages

Re: btrfs: why default 4M readahead size?

2010-03-18 Thread Shaohua Li
On Thu, Mar 18, 2010 at 08:53:13PM +0800, Chris Mason wrote: > On Thu, Mar 18, 2010 at 09:42:57AM +0800, Shaohua Li wrote: > > Btrfs uses below equation to calculate ra_pages: > > fs_info->bdi.ra_pages = max(fs_info->bdi.ra_pages, > > 4 * 1024 * 1024 / PAGE_CACHE_SIZ

Re: btrfs: why default 4M readahead size?

2010-03-18 Thread Chris Mason
On Thu, Mar 18, 2010 at 09:42:57AM +0800, Shaohua Li wrote: > Btrfs uses below equation to calculate ra_pages: > fs_info->bdi.ra_pages = max(fs_info->bdi.ra_pages, > 4 * 1024 * 1024 / PAGE_CACHE_SIZE); > is the max() a typo of min()? This makes the readahead size

btrfs: why default 4M readahead size?

2010-03-17 Thread Shaohua Li
Btrfs uses below equation to calculate ra_pages: fs_info->bdi.ra_pages = max(fs_info->bdi.ra_pages, 4 * 1024 * 1024 / PAGE_CACHE_SIZE); is the max() a typo of min()? This makes the readahead size is 4M by default, which is too big. I have a system with 16 CPU, 6G mem