From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 22 Oct 2007 09:11:13 -0400 From: Chris Mason Subject: Re: [PATCH] rd: Use a private inode for backing storage Message-ID: <20071022091113.0343602a@think.oraclecorp.com> In-Reply-To: References: <200710151028.34407.borntraeger@de.ibm.com> <200710210928.58265.borntraeger@de.ibm.com> <200710211956.50624.nickpiggin@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: "Eric W. Biederman" Cc: Nick Piggin , Christian Borntraeger , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Martin Schwidefsky , Theodore Ts'o , stable@kernel.org List-ID: On Sun, 21 Oct 2007 12:39:30 -0600 ebiederm@xmission.com (Eric W. Biederman) wrote: > Nick Piggin writes: > > > On Sunday 21 October 2007 18:23, Eric W. Biederman wrote: > >> Christian Borntraeger writes: > > > >> Let me put it another way. Looking at /proc/slabinfo I can get > >> 37 buffer_heads per page. I can allocate 10% of memory in > >> buffer_heads before we start to reclaim them. So it requires just > >> over 3.7 buffer_heads on very page of low memory to even trigger > >> this case. That is a large 1k filesystem or a weird sized > >> partition, that we have written to directly. > > > > On a highmem machine it it could be relatively common. > > Possibly. But the same proportions still hold. 1k filesystems > are not the default these days and ramdisks are relatively uncommon. > The memory quantities involved are all low mem. It is definitely common during run time. It was seen in practice enough to be reproducible and get fixed for the non-ramdisk case. The big underlying question is how which ramdisk usage case are we shooting for. Keeping the ram disk pages off the LRU can certainly help the VM if larger ramdisks used at runtime are very common. Otherwise, I'd say to keep it as simple as possible and use Eric's patch. By simple I'm not counting lines of code, I'm counting overall readability between something everyone knows (page cache usage) and something specific to ramdisks (Nick's patch). -chris -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org