From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 27 Sep 2016 21:24:58 +1000 From: Nicholas Piggin To: Vlastimil Babka Cc: Jason Baron , Hillf Danton , 'Alexander Viro' , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, 'Michal Hocko' , netdev@vger.kernel.org, Eric Dumazet Subject: Re: [PATCH] fs/select: add vmalloc fallback for select(2) Message-ID: <20160927212458.3ab42b41@roar.ozlabs.ibm.com> In-Reply-To: <5014387d-43da-03f6-a74b-2dc4fbf4fe32@suse.cz> References: <20160922152831.24165-1-vbabka@suse.cz> <006101d21565$b60a8a70$221f9f50$@alibaba-inc.com> <20160923172434.7ad8f2e0@roar.ozlabs.ibm.com> <57E55CBB.5060309@akamai.com> <5014387d-43da-03f6-a74b-2dc4fbf4fe32@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: On Tue, 27 Sep 2016 10:44:04 +0200 Vlastimil Babka wrote: > On 09/23/2016 06:47 PM, Jason Baron wrote: > > Hi, > > > > On 09/23/2016 03:24 AM, Nicholas Piggin wrote: > >> On Fri, 23 Sep 2016 14:42:53 +0800 > >> "Hillf Danton" wrote: > >> > >>>> > >>>> The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows > >>>> with the number of fds passed. We had a customer report page allocation > >>>> failures of order-4 for this allocation. This is a costly order, so it might > >>>> easily fail, as the VM expects such allocation to have a lower-order fallback. > >>>> > >>>> Such trivial fallback is vmalloc(), as the memory doesn't have to be > >>>> physically contiguous. Also the allocation is temporary for the duration of the > >>>> syscall, so it's unlikely to stress vmalloc too much. > >>>> > >>>> Note that the poll(2) syscall seems to use a linked list of order-0 pages, so > >>>> it doesn't need this kind of fallback. > >> > >> How about something like this? (untested) > > This pushes the limit further, but might just delay the problem. Could be an > optimization on top if there's enough interest, though. What's your customer doing with those selects? If they care at all about performance, I doubt they want select to attempt order-4 allocations, fail, then use vmalloc :) -- 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