lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 8 Aug 2013 12:18:07 +0200 From: Jan Kara <jack@...e.cz> To: Andy Lutomirski <luto@...capital.net> Cc: Dave Hansen <dave.hansen@...el.com>, Jan Kara <jack@...e.cz>, linux-mm@...ck.org, linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [RFC 0/3] Add madvise(..., MADV_WILLWRITE) On Wed 07-08-13 11:00:52, Andy Lutomirski wrote: > On Wed, Aug 7, 2013 at 10:40 AM, Dave Hansen <dave.hansen@...el.com> wrote: > > On 08/07/2013 06:40 AM, Jan Kara wrote: > >> One question before I look at the patches: Why don't you use fallocate() > >> in your application? The functionality you require seems to be pretty > >> similar to it - writing to an already allocated block is usually quick. > > > > One problem I've seen is that it still costs you a fault per-page to get > > the PTEs in to a state where you can write to the memory. MADV_WILLNEED > > will do readahead to get the page cache filled, but it still leaves the > > pages unmapped. Those faults get expensive when you're trying to do a > > couple hundred million of them all at once. > > I have grand plans to teach the kernel to use hardware dirty tracking > so that (some?) pages can be left clean and writable for long periods > of time. This will be hard. Right that will be tough... Although with your application you could require such pages to be mlocked and then I could imagine we would get away at least from problems with dirty page accounting. > Even so, the second write fault to a page tends to take only a few > microseconds, while the first one often blocks in fs code. So you wrote blocks are already preallocated with fallocate(). If you also preload pages in memory with MADV_WILLNEED is there still big difference between the first and subsequent write fault? > (mmap_sem is a different story, but I see it as a separate issue.) Yeah, agreed. Honza -- Jan Kara <jack@...e.cz> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists