linux-kernel - Re: [PATCH] mm: Move readahead limit outside of readahead, and advisory syscalls

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

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 25 Jul 2016 13:47:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kyle Walker <kwalker@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Michal Hocko <mhocko@...e.com>,
	Geliang Tang <geliangtang@....com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Roman Gushchin <klamm@...dex-team.ru>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] mm: Move readahead limit outside of readahead, and
 advisory syscalls

On Mon, 25 Jul 2016 10:39:25 -0400 Kyle Walker <kwalker@...hat.com> wrote:

> Java workloads using the MappedByteBuffer library result in the fadvise()
> and madvise() syscalls being used extensively. Following recent readahead
> limiting alterations, such as 600e19af ("mm: use only per-device readahead
> limit") and 6d2be915 ("mm/readahead.c: fix readahead failure for
> memoryless NUMA nodes and limit readahead pages"), application performance
> suffers in instances where small readahead is configured.

Can this suffering be quantified please?

> By moving this limit outside of the syscall codepaths, the syscalls are
> able to advise an inordinately large amount of readahead when desired.
> With a cap being imposed based on the half of NR_INACTIVE_FILE and
> NR_FREE_PAGES. In essence, allowing performance tuning efforts to define a
> small readahead limit, but then benefiting from large sequential readahead
> values selectively.
> 
> ...
>
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -211,7 +211,9 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
>  	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
>  		return -EINVAL;
>  
> -	nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages);
> +	nr_to_read = min(nr_to_read, (global_page_state(NR_INACTIVE_FILE) +
> +				     (global_page_state(NR_FREE_PAGES)) / 2));
> +
>  	while (nr_to_read) {
>  		int err;
>  
> @@ -484,6 +486,7 @@ void page_cache_sync_readahead(struct address_space *mapping,
>  
>  	/* be dumb */
>  	if (filp && (filp->f_mode & FMODE_RANDOM)) {
> +		req_size = min(req_size, inode_to_bdi(mapping->host)->ra_pages);
>  		force_page_cache_readahead(mapping, filp, offset, req_size);
>  		return;
>  	}

Linus probably has opinions ;)