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Date: Wed, 13 Feb 2019 09:31:03 -0800 From: Eric Dumazet <eric.dumazet@...il.com> To: Stefano Brivio <sbrivio@...hat.com> Cc: Stephen Hemminger <stephen@...workplumber.org>, netdev@...r.kernel.org, Sabrina Dubroca <sd@...asysnail.net> Subject: Re: [PATCH iproute2 net-next v2 3/4] ss: Buffer raw fields first, then render them as a table On 02/13/2019 12:37 AM, Stefano Brivio wrote: > On Tue, 12 Feb 2019 16:42:04 -0800 > Eric Dumazet <eric.dumazet@...il.com> wrote: > >> I do not get it. >> >> "ss -emoi " uses almost 1KB per socket. >> >> 10,000,000 sockets -> we need about 10GB of memory ??? >> >> This is a serious regression. > > I guess this is rather subjective: the worst case I considered back then > was the output of 'ss -tei0' (less than 500 bytes) for one million > sockets, which gives 500M of memory, which should in turn be fine on a > machine handling one million sockets. > > Now, if 'ss -emoi' on 10 million sockets is an actual use case (out of > curiosity: how are you going to process that output? Would JSON help?), > I see two easy options to solve this: ss -temoi | parser (written in shell or awk or whatever...) This is a use case, I just got bitten because using ss command actually OOM my container, while trying to debug a busy GFE. The host itself can have 10,000,000 TCP sockets, but usually sysadmin shells run in a container with no more than 500 MB available. Otherwise, it would be too easy for a buggy program to OOM the whole machine and have angry customers. > > 1. flush the output every time we reach a given buffer size (1M > perhaps). This might make the resulting blocks slightly unaligned, > with occasional loss of readability on lines occurring every 1k to > 10k sockets approximately, even though after 1k sockets column sizes > won't change much (it looks anyway better than the original), and I > don't expect anybody to actually scroll that output > > 2. add a switch for unbuffered output, but then you need to remember to > pass it manually, and the whole output would be as bad as the > original in case you need the switch. > > I'd rather go with 1., it's easy to implement (we already have partial > flushing with '--events') and it looks like a good compromise on > usability. Thoughts? > 1 seems fine, but a switch for 'please do not try to format' would be fine. I wonder why we try to 'format' when stdout is a pipe or a regular file .
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