Re: [PATCH] mm: use only per-device readahead limit

2015-08-21 Thread Linus Torvalds
On Fri, Aug 21, 2015 at 1:21 PM, Roman Gushchin wrote: > > It's just a raid driver. For instance, drivers/md/raid5.c:6898 . Ok. That makes me a bit less nervous. I was worried there was some admin program out there that just ups the readahead on peoples devices, which would mean that ra_pages is

Re: [PATCH] mm: use only per-device readahead limit

2015-08-21 Thread Roman Gushchin
21.08.2015, 21:17, "Linus Torvalds" : > On Fri, Aug 21, 2015 at 10:12 AM, Roman Gushchin wrote: >>  There are devices, which require custom readahead limit. >>  For instance, for RAIDs it's calculated as number of devices >>  multiplied by chunk size times 2. > > So afaik, the default read-ahead s

Re: [PATCH] mm: use only per-device readahead limit

2015-08-21 Thread Linus Torvalds
On Fri, Aug 21, 2015 at 10:12 AM, Roman Gushchin wrote: > > There are devices, which require custom readahead limit. > For instance, for RAIDs it's calculated as number of devices > multiplied by chunk size times 2. So afaik, the default read-ahead size is 128kB, which is actually smaller than th

[PATCH] mm: use only per-device readahead limit

2015-08-21 Thread Roman Gushchin
Maximal readahead size is limited now by two values: 1) by global 2Mb constant (MAX_READAHEAD in max_sane_readahead()) 2) by configurable per-device value* (bdi->ra_pages) There are devices, which require custom readahead limit. For instance, for RAIDs it's calculated as number of devices multipli