From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 10 Aug 2017 13:38:31 +0900 From: Minchan Kim To: Daniel Colascione , Andrew Morton Cc: linux-kernel@vger.kernel.org, timmurray@google.com, joelaf@google.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , sonnyrao@chromium.org, robert.foss@collabora.com Subject: Re: [PATCH RFC v2] Add /proc/pid/smaps_rollup Message-ID: <20170810043831.GB2249@bbox> References: <20170808132554.141143-1-dancol@google.com> <20170810001557.147285-1-dancol@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170810001557.147285-1-dancol@google.com> Sender: owner-linux-mm@kvack.org List-ID: On Wed, Aug 09, 2017 at 05:15:57PM -0700, Daniel Colascione wrote: > /proc/pid/smaps_rollup is a new proc file that improves the > performance of user programs that determine aggregate memory > statistics (e.g., total PSS) of a process. > > Android regularly "samples" the memory usage of various processes in > order to balance its memory pool sizes. This sampling process involves > opening /proc/pid/smaps and summing certain fields. For very large > processes, sampling memory use this way can take several hundred > milliseconds, due mostly to the overhead of the seq_printf calls in > task_mmu.c. > > smaps_rollup improves the situation. It contains most of the fields of > /proc/pid/smaps, but instead of a set of fields for each VMA, > smaps_rollup instead contains one synthetic smaps-format entry > representing the whole process. In the single smaps_rollup synthetic > entry, each field is the summation of the corresponding field in all > of the real-smaps VMAs. Using a common format for smaps_rollup and > smaps allows userspace parsers to repurpose parsers meant for use with > non-rollup smaps for smaps_rollup, and it allows userspace to switch > between smaps_rollup and smaps at runtime (say, based on the > availability of smaps_rollup in a given kernel) with minimal fuss. > > By using smaps_rollup instead of smaps, a caller can avoid the > significant overhead of formatting, reading, and parsing each of a > large process's potentially very numerous memory mappings. For > sampling system_server's PSS in Android, we measured a 12x speedup, > representing a savings of several hundred milliseconds. > > One alternative to a new per-process proc file would have been > including PSS information in /proc/pid/status. We considered this > option but thought that PSS would be too expensive (by a few orders of > magnitude) to collect relative to what's already emitted as part of > /proc/pid/status, and slowing every user of /proc/pid/status for the > sake of readers that happen to want PSS feels wrong. > > The code itself works by reusing the existing VMA-walking framework we > use for regular smaps generation and keeping the mem_size_stats > structure around between VMA walks instead of using a fresh one for > each VMA. In this way, summation happens automatically. We let > seq_file walk over the VMAs just as it does for regular smaps and just > emit nothing to the seq_file until we hit the last VMA. > > Patch changelog: > > v2: Fix typo in commit message > Add ABI documentation as requested by gregkh > > Signed-off-by: Daniel Colascione I love this. FYI, there was trial but got failed at that time so in this time, https://marc.info/?l=linux-kernel&m=147310650003277&w=2 http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1229163.html I really hope we merge this patch. -- 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