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In [Link] Linus mentions that acquire/release makes it clear which _particular_ memory accesses are the ordered ones, and it's unlikely to make any performance difference, so it's much better to pair up the release->acquire ordering than have a "wmb->rmb" ordering. ========================================================= update pagecache folio_mark_uptodate(folio) smp_wmb() set_bit PG_uptodate === ↑↑↑ STLR ↑↑↑ === smp_store_release(&inode->i_size, i_size) folio_test_uptodate(folio) test_bit PG_uptodate smp_rmb() === ↓↓↓ LDAR ↓↓↓ === smp_load_acquire(&inode->i_size) copy_page_to_iter() ========================================================= Calling smp_store_release() in i_size_write() ensures that the data in the page and the PG_uptodate bit are updated before the isize is updated, and calling smp_load_acquire() in i_size_read ensures that it will not read a newer isize than the data in the page. Therefore, this avoids buffered read-write inconsistencies caused by Load-Load reordering. Link: https://lore.kernel.org/r/CAHk-=wifOnmeJq+sn+2s-P46zw0SFEbw9BSCGgp2c5fYPtRPGw@mail.gmail.com/ Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Baokun Li <libaokun1@huawei.com> Link: https://lore.kernel.org/r/20240124142857.4146716-2-libaokun1@huawei.com Signed-off-by: Christian Brauner <brauner@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.