|From:||Linus Torvalds <torvalds-AT-linux-foundation.org>|
|To:||"Artem S. Tashkinov" <t.artem-AT-lycos.com>, Wu Fengguang <fengguang.wu-AT-intel.com>, Andrew Morton <akpm-AT-linux-foundation.org>|
|Subject:||Re: Disabling in-memory write cache for x86-64 in Linux II|
|Date:||Fri, 25 Oct 2013 09:18:49 +0100|
|Cc:||Linux Kernel Mailing List <linux-kernel-AT-vger.kernel.org>, linux-fsdevel <linux-fsdevel-AT-vger.kernel.org>, Jens Axboe <axboe-AT-kernel.dk>, linux-mm <linux-mm-AT-kvack.org>|
On Fri, Oct 25, 2013 at 8:25 AM, Artem S. Tashkinov <email@example.com> wrote: > > On my x86-64 PC (Intel Core i5 2500, 16GB RAM), I have the same 3.11 kernel > built for the i686 (with PAE) and x86-64 architectures. What's really troubling me > is that the x86-64 kernel has the following problem: > > When I copy large files to any storage device, be it my HDD with ext4 partitions > or flash drive with FAT32 partitions, the kernel first caches them in memory entirely > then flushes them some time later (quite unpredictably though) or immediately upon > invoking "sync". Yeah, I think we default to a 10% "dirty background memory" (and allows up to 20% dirty), so on your 16GB machine, we allow up to 1.6GB of dirty memory for writeout before we even start writing, and twice that before we start *waiting* for it. On 32-bit x86, we only count the memory in the low 1GB (really actually up to about 890MB), so "10% dirty" really means just about 90MB of buffering (and a "hard limit" of ~180MB of dirty). And that "up to 3.2GB of dirty memory" is just crazy. Our defaults come from the old days of less memory (and perhaps servers that don't much care), and the fact that x86-32 ends up having much lower limits even if you end up having more memory. You can easily tune it: echo $((16*1024*1024)) > /proc/sys/vm/dirty_background_bytes echo $((48*1024*1024)) > /proc/sys/vm/dirty_bytes or similar. But you're right, we need to make the defaults much saner. Wu? Andrew? Comments? Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to firstname.lastname@example.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"email@example.com"> firstname.lastname@example.org </a>
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