linux-kernel - [PATCH] fs/proc: add VmTaskSize field to /proc/$$/status

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Message-Id: <1556225867-458-1-git-send-email-jsavitz@redhat.com>
Date:   Thu, 25 Apr 2019 16:57:47 -0400
From:   Joel Savitz <jsavitz@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Joel Savitz <jsavitz@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ram Pai <linuxram@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Huang Ying <ying.huang@...el.com>,
        Sandeep Patil <sspatil@...roid.com>,
        Rafael Aquini <aquini@...hat.com>,
        linux-fsdevel@...r.kernel.org
Subject: [PATCH] fs/proc: add VmTaskSize field to /proc/$$/status

Currently, there is no fast mechanism to get the virtual memory size of
the current process from userspace. This information is available to the
user through several means, one being a linear search of the entire address
space. This is the method used by a component of the libhugetlb kernel
test, and using the mechanism proposed in this patch, the time complexity
of that test would be upgraded to constant time from linear time. This is
especially relevant on 64-bit architechtures where a linear search of
the address space could take an absurd amount of time. Using this
mechanism, the modification to the test component would be portable
across all architechtures.

Signed-off-by: Joel Savitz <jsavitz@...hat.com>
---
 fs/proc/task_mmu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 92a91e7816d8..f64b9a949624 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -74,7 +74,10 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
 	seq_put_decimal_ull_width(m,
 		    " kB\nVmPTE:\t", mm_pgtables_bytes(mm) >> 10, 8);
 	SEQ_PUT_DEC(" kB\nVmSwap:\t", swap);
-	seq_puts(m, " kB\n");
+	SEQ_PUT_DEC(" kB\nVmSwap:\t", swap);
+	seq_put_decimal_ull_width(m,
+		    " kB\nVmTaskSize:\t", TASK_SIZE >> 10, 8);
+	seq_puts(m, " kB\n");
 	hugetlb_report_usage(m, mm);
 }
 #undef SEQ_PUT_DEC
-- 
2.18.1