On Sun, Jan 26, 2020 at 9:15 AM Pavel Machek <pavel@xxxxxxx> wrote: > > On Fri 2020-01-24 10:32:49, Greg Kroah-Hartman wrote: > > From: Eric Dumazet <edumazet@xxxxxxxxxx> > > > > [ Upstream commit 503978aca46124cd714703e180b9c8292ba50ba7 ] > > > > As mentioned in https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance > > a C compiler can legally transform : > > > > if (memory_pressure && *memory_pressure) > > *memory_pressure = 0; > > > > to : > > > > if (memory_pressure) > > *memory_pressure = 0; > > Well, C compiler can do a lot of stuff, and we rely on C compiler > being "sane" -- that is gcc. > > Even if compiler did the transformation, that will only result in > slightly slower performance, right? > > Is there any evidence this is problem in practice? Should this be in > stable? There is evidence of this problem in practice yes. Should it be in stable I do not know. Should stable kernels only be compiled by old compilers, I do not know.
