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b=fPJbXbpYAQYSCAwmqqgmXLxZlU6TDzdhxRZOEgK/ypHcmb/jfRuwBZWIq5t4Gokz7 b8gzGWla2B/ptCjddFSETIb77LWDOD4/oXEBDyhHN6ecbw0IfvRCGtwIfnriwBWDxh JoXKH770DkJSwE5DEyP3KMSBTizK+866lgrzWwdi+gT3HFz3RKGgajeH6HsAiN7341 F5C1bBaCIV3SZx0RjgnZUfqxmW8K4ZjMEPon8zUb6uVeq3cYHCJfUad6nhqXY8Zp88 ESU6RLSMkAWzwYlUIfLcjis0B0g+63qYq8cmazpzqNC9N3Z+DxFgrLqnvTnriX/5OG k/nSvpQWTdLag== From: SeongJae Park To: Zhen Ni Cc: SeongJae Park , akpm@linux-foundation.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/3] mm/page_owner: add print_mode filter Date: Fri, 8 May 2026 17:29:01 -0700 Message-ID: <20260509002902.83937-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260507064643.179187-2-zhen.ni@easystack.cn> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: uuwqiie9dxgw5watejr7xopt13z19m5i X-Rspam-User: X-Rspamd-Queue-Id: 04841A0008 X-Rspamd-Server: rspam07 X-HE-Tag: 1778286551-906287 X-HE-Meta: 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 K5PirAug iGrzXQrJq2/lrqWvz5k08Jqu3woktWBJDN66WgG7HOhyO75Ol9i7FBJ4XX8nGPuppbkZKtNfLSSFij9mThufECAHwAVII0AKjV+op2yCr1BOaAlcbCdxAHUDmwwrJpsbmkHkpXuByWf88lh3jr0dqIRSeGeZYgGyva/ZVhiSva5zdiR39KWCrbOLo7RVeBcWK2Dxu2UhEzvuCqXbt/H/FeABtGCIBGrP2sUMdogG7uiZfiTkqKvASg2c9DZqSupwzNURsSUiZzeIEudmORIggux+dgCtqwD8vm+t5ISTj2umNe/Wvcksy2eRjIghPVYfuOSPGbsmtW2FLUbY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 7 May 2026 14:46:41 +0800 Zhen Ni wrote: > Add a print_mode filter to page_owner that allows users to choose between > printing full stack traces or only stack handles, significantly reducing > output size for debugging and analysis. > > The filter provides a string-based interface under > /sys/kernel/debug/page_owner_filter/: > - Reading shows the current mode with [] brackets around active option > - Writing accepts "full_stack" or "stack_handle" strings > > The default full_stack mode maintains backward compatibility with existing > usage, displaying complete stack traces for each page allocation. > > The stack_handle mode dramatically reduces log size by showing only > the handle number instead of the full stack trace. The mapping from > handles to actual stack traces can be obtained via the > show_stacks_handles interface. > > Example usage: > # echo stack_handle > /sys/kernel/debug/page_owner_filter/print_mode > # cat /sys/kernel/debug/page_owner_filter/print_mode > full_stack [stack_handle] > # cat /sys/kernel/debug/page_owner > Page allocated via order 0, migratetype Unmovable, gfp_mask 0x1100ca, > pid 1, tgid 1 (systemd), ts 123456789 ns > PFN 0x1000 type Unmovable Block 1 type Unmovable > Flags 0x3fffe800000084(referenced|lru|active|private|node=0|zone=1) > handle: 17432583 > ... > > Signed-off-by: Zhen Ni I added a few trivial comments below, but overall looks good to me. Reviewed-by: SeongJae Park > --- > > Changes in v5: > - No code changes > > Changes in v4: > - Change from numeric (0/1) to string-based interface ("full_stack"/"stack_handle") > - Merge infrastructure patch into this patch > > Changes in v3: > - No code changes > > Changes in v2: > - Renamed from 'compact mode' to 'print_mode' for better clarity > - Use enum values (0=full_stack, 1=stack_handle) instead of boolean > - Update debugfs filename from 'compact' to 'print_mode' Adding links to previous revisions would be helpful. > --- > mm/page_owner.c | 93 +++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 91 insertions(+), 2 deletions(-) > > diff --git a/mm/page_owner.c b/mm/page_owner.c > index 8178e0be557f..28766c854d02 100644 > --- a/mm/page_owner.c > +++ b/mm/page_owner.c [...] > @@ -575,7 +594,11 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, > migratetype_names[pageblock_mt], > &page->flags); > > - ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0); > + if (READ_ONCE(owner_filter.print_mode) == PAGE_OWNER_PRINT_STACK_HANDLE) { > + ret += scnprintf(kbuf + ret, count - ret, > + "handle: %d\n", handle); > + } else > + ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0); Braces are unnecessary [2] because both branches have only one statement. [...] > +static ssize_t print_mode_write(struct file *file, > + const char __user *buf, > + size_t count, loff_t *ppos) > +{ > + char *kbuf; > + int mode; > + int ret = count; > + > + /* > + * Limit input size. Maximum valid input is "stack_handle" (12 chars) > + * plus newline and null terminator. Use 32 bytes as a reasonable limit. > + */ > + if (count > 32) > + return -EINVAL; > + > + kbuf = kmalloc(count + 1, GFP_KERNEL); > + if (!kbuf) > + return -ENOMEM; Would it make sense to use kmalloc_objs(), or simply using a local array as Andrew suggested? [...] [1] https://docs.kernel.org/process/submitting-patches.html#commentary [2] https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces Thanks, SJ