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From 0fc51b569570e8bf5aecd5ee03a88eb668b7b385 Mon Sep 17 00:00:00 2001
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From: Anita Zhang <the.anitazha@gmail.com>
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Date: Tue, 14 Sep 2021 16:33:10 -0700
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Subject: [PATCH] fileio: start with 4k buffer for procfs
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There's a very gradual increase of anonymous memory in systemd-journald that
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blames to 2ac67221bb6270f0fbe7cbd0076653832cd49de2.
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systemd-journald makes many calls to read /proc/PID/cmdline and
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/proc/PID/status, both of which tend to be well under 4K. However the
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combination of allocating 4M read buffers, then using `realloc()` to
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shrink the buffer in `read_virtual_file()` appears to be creating
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fragmentation in the heap (when combined with the other allocations
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systemd-journald is doing).
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To help mitigate this, try reading /proc with a 4K buffer as
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`read_virtual_file()` did before 2ac67221bb6270f0fbe7cbd0076653832cd49de2.
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If it isn't big enough then try again with the larger buffers.
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---
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src/basic/fileio.c | 5 +++++
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1 file changed, 5 insertions(+)
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diff --git a/src/basic/fileio.c b/src/basic/fileio.c
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index 99a44fdea2..466c6321c7 100644
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--- a/src/basic/fileio.c
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+++ b/src/basic/fileio.c
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@@ -431,6 +431,11 @@ int read_virtual_file(const char *filename, size_t max_size, char **ret_contents
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}
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n_retries--;
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+ } else if (n_retries > 1) {
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+ /* Files in /proc are generally smaller than the page size so let's start with a page size
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+ * buffer from malloc and only use the max buffer on the final try. */
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+ size = MIN3(page_size() - 1, READ_VIRTUAL_BYTES_MAX, max_size);
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+ n_retries = 1;
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} else {
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size = MIN(READ_VIRTUAL_BYTES_MAX, max_size);
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n_retries = 0;
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--
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2.31.1
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