| Message ID | 20241015133016.23468-1-ddiss@suse.de (mailing list archive) |
|---|---|
| Headers | show |
| Series | initramfs: reduce buffer footprint | expand |
On Tue, Oct 15, 2024 at 01:11:57PM +0000, David Disseldorp wrote: > There are a number of stack, heap and data-segment buffers which are > unnecessary for initramfs unpacking. This patchset attempts to remove > them by: > - parsing cpio hex strings in place, instead of copying them for > nul-termination. (Patches 1 & 2). > - reusing a single heap buffer for cpio header, file and symlink paths, > instead of three separate buffers. (Patches 3 & 4). > - reusing the heap-allocated cpio buffer across both builtin and > bootloader-provided unpack attempts. (Patch 5). > - reusing the heap-allocated cpio buffer for error messages on > FSM-exit, instead of a data-segment buffer. (Patch 6). > > I've flagged this as an RFC as I'd like to improve the commit messages > and also provide more thorough testing, likely via kunit / kselftest > integration. Umm... An obvious question: what's the point? Reducing the amount of temporary allocations (and not particularly large ones, at that) done during early boot and freed before we run anything in user mode?
On Wed, 16 Oct 2024 00:34:15 +0100, Al Viro wrote: > On Tue, Oct 15, 2024 at 01:11:57PM +0000, David Disseldorp wrote: > > There are a number of stack, heap and data-segment buffers which are > > unnecessary for initramfs unpacking. This patchset attempts to remove > > them by: > > - parsing cpio hex strings in place, instead of copying them for > > nul-termination. (Patches 1 & 2). > > - reusing a single heap buffer for cpio header, file and symlink paths, > > instead of three separate buffers. (Patches 3 & 4). > > - reusing the heap-allocated cpio buffer across both builtin and > > bootloader-provided unpack attempts. (Patch 5). > > - reusing the heap-allocated cpio buffer for error messages on > > FSM-exit, instead of a data-segment buffer. (Patch 6). > > > > I've flagged this as an RFC as I'd like to improve the commit messages > > and also provide more thorough testing, likely via kunit / kselftest > > integration. > > Umm... An obvious question: what's the point? Reducing the amount of > temporary allocations (and not particularly large ones, at that) done > during early boot and freed before we run anything in user mode? "reduce buffer footprint" is a bad title... My initial motivation was to improve initramfs unpack error reporting (still WIP), following a downstream bug report. Patches 1 & 2 avoid 13 memcpy() calls for every initramfs entry and IMO leave the code more readable, so should be justified once I have profiling data. Patches 3-5 remove five extra kmalloc() calls when booting with built-in and bootloader initramfses. I doubt it'll be visible in profiling, but they allow for buffer reuse for dynamic error messages instead of sprinkling data-segment buffers around, like the one removed in patch 6.
There are a number of stack, heap and data-segment buffers which are unnecessary for initramfs unpacking. This patchset attempts to remove them by: - parsing cpio hex strings in place, instead of copying them for nul-termination. (Patches 1 & 2). - reusing a single heap buffer for cpio header, file and symlink paths, instead of three separate buffers. (Patches 3 & 4). - reusing the heap-allocated cpio buffer across both builtin and bootloader-provided unpack attempts. (Patch 5). - reusing the heap-allocated cpio buffer for error messages on FSM-exit, instead of a data-segment buffer. (Patch 6). I've flagged this as an RFC as I'd like to improve the commit messages and also provide more thorough testing, likely via kunit / kselftest integration. Feedback appreciated. David Disseldorp (6): vsprintf: add simple_strntoul initramfs: avoid memcpy for hex header fields initramfs: remove extra symlink path buffer initramfs: merge header_buf and name_buf initramfs: reuse buf for built-in and bootloader initramfs initramfs: avoid static buffer for error message include/linux/kstrtox.h | 1 + init/initramfs.c | 50 +++++++++++++++++++++-------------------- lib/vsprintf.c | 7 ++++++ 3 files changed, 34 insertions(+), 24 deletions(-)