Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH] fs: optimise generic_write_check_limits() | Date | Sun, 8 Aug 2021 14:41:13 +0000 |
| |
From: Matthew Wilcox > Sent: 06 August 2021 14:28 > > On Fri, Aug 06, 2021 at 12:22:10PM +0100, Pavel Begunkov wrote: > > Even though ->s_maxbytes is used by generic_write_check_limits() only in > > case of O_LARGEFILE, the value is loaded unconditionally, which is heavy > > and takes 4 indirect loads. Optimise it by not touching ->s_maxbytes, > > if it's not going to be used. > > Is this "optimisation" actually worth anything? Look at how > force_o_largefile() is used. I would suggest that on the vast majority > of machines, O_LARGEFILE is always set.
An option would be to only determine ->s_maxbytes when the size if larger than MAX_NON_LFS.
So you'd end up with something like:
if (pos >= max_size) { if (!(file->f_flags & O_LARGEFILE)) return -EFBIG; inode = file->f_mapping->host; if (pos >= inode->i_sb->s_maxbytes) return -EFBIG; }
David
- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
| |