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Shutemov" Subject: Re: [PATCH v2] mm/khugepaged: add tracepoint to collapse_file() Message-ID: References: <20221024173559.332324-1-gautammenghani201@gmail.com> <20221024131706.3d58bd92c332684386c7df13@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221024131706.3d58bd92c332684386c7df13@linux-foundation.org> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666674319; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=3cbUiytZCvIodwgXeI/vSOQye/5S1njVlXadTLjeUo8=; b=2ZpKtl4jxbErur8Ja0IJ2Rjf3ZD42Ur6oZeE/xAh2BHknGIHX5p1bPrd2/8RlllVn/7Ph6 JcBiPog669+F5+2ToveKdEq3u+tMBcXJvVhbOcbeU82yGq8v6pmbG0+5KMovVRVrJEpfLY BYUtRKMCJUEqcY2z2C1NXHDQ2E1nZEU= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=W5kfkuG9; spf=pass (imf09.hostedemail.com: domain of gautammenghani201@gmail.com designates 209.85.210.171 as permitted sender) smtp.mailfrom=gautammenghani201@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666674319; a=rsa-sha256; cv=none; b=TrfRBnhC67MuP6JU5KMFZSRuSHM3oT/lqAWWnpS/VLDwtKU15nZjSj1TY9IoBLTFnsz88R VJaIAjdWUTgE8Fl+4SlS3e8sxhPIx/fzq5rQqHSFIxF5UNvq3kHaS1C8Tiix1QRfZUGk/x nmo3qXm/FYoNVVeZACJklQXmiFwbtAc= Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=W5kfkuG9; spf=pass (imf09.hostedemail.com: domain of gautammenghani201@gmail.com designates 209.85.210.171 as permitted sender) smtp.mailfrom=gautammenghani201@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Stat-Signature: ju3fufkcyiupjx8cn1t8o78io3grcdic X-Rspamd-Queue-Id: 8433F140012 X-Rspamd-Server: rspam07 X-Rspam-User: X-HE-Tag: 1666674319-432868 X-Bogosity: Ham, tests=bogofilter, spamicity=0.019650, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Oct 24, 2022 at 01:17:06PM -0700, Andrew Morton wrote: > On Mon, 24 Oct 2022 23:05:58 +0530 Gautam Menghani wrote: > > > In the file mm/khugepaged.c, a TODO in the function collapse_file() asks > > to add tracepoints. Add the tracepoint named "mm_khugepaged_collapse_file". > > This isn't a very satisfying explanation for changing the kernel. Maybe > the comment is stale are this tracepoint is unneeded. > > Please explain afresh how this addition benefits kernel users? > The function collapse_file() is called by the function hpage_collapse_scan_file(). Without a tracepoint in collapse_file(), we won't know if it was called or not and as a result, we also won't know if it returned successfully or not. Also, as Zach mentioned earlier [1]: there are a few scan result codes that overlap between hpage_collapse_scan_file() and those possibly returned in collapse_file() such that, if we only have the one tracepoint in hpage_collapse_scan_file(), it could be ambiguous what callsite the error path stemmed from. [1]:https://lore.kernel.org/lkml/CAAa6QmSKtj6T2dW1tkg5_HVj2+rXj5inOLdEzr0MkJzQxxcPXQ@mail.gmail.com/ Please do let me know if a v3 is needed. Thanks, Gautam