linux-kernel - Re: [PATCH 8/9] tmpfs: radix_tree

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] [day] [month] [year] [list]

Date:	Wed, 19 Dec 2007 07:50:49 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Rohland <hans-christoph.rohland@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] tmpfs: radix_tree_preloading

On Tue, Dec 18, 2007 at 10:05:19PM +0000, Hugh Dickins wrote:
> Nick has observed that shmem.c still uses GFP_ATOMIC when adding to page
> cache or swap cache, without any radix tree preload: so tending to deplete
> emergency reserves of memory.
> 
> GFP_ATOMIC remains appropriate in shmem_writepage's add_to_swap_cache:
> it's being called under memory pressure, so must not wait for more memory
> to become available.  But shmem_unuse_inode now has a window in which it
> can and should preload with GFP_KERNEL, and say GFP_NOWAIT instead of
> GFP_ATOMIC in its add_to_page_cache.
> 
> shmem_getpage is not so straightforward: its filepage/swappage integrity
> relies upon exchanging between caches under spinlock, and it would need a
> lot of restructuring to place the preloads correctly.  Instead, follow
> its pattern of retrying on races: use GFP_NOWAIT instead of GFP_ATOMIC in
> add_to_page_cache, and begin each circuit of the repeat loop with a sleeping
> radix_tree_preload, followed immediately by radix_tree_preload_end - that
> won't guarantee success in the next add_to_page_cache, but doesn't need to.
> 
> And we can then remove that bothersome congestion_wait: when needed,
> it'll automatically get done in the course of the radix_tree_preload.
> 
> Signed-off-by: Hugh Dickins <hugh@...itas.com>

Looks good to me. Thanks for this!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/