Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 于2021年6月8日周二 下午5:29写道： > > On Mon, Jun 07, 2021 at 08:39:14AM -0700, yongw.pur@xxxxxxxxx wrote: > > From: wangyong <wang.yong12@xxxxxxxxxx> > > > > When zram is used, available+Swap free memory is obviously bigger than we > > actually can use, because zram can compress memory by compression > > algorithm and zram compressed data will occupy memory too. > > > > So, we can count the compression ratio of zram in the kernel. The space > > will be saved by zram and other swap device are calculated as follows: > > zram[swapfree - swapfree * compress ratio] + swapdev[swapfree] > > We can evaluate the available memory of the whole system as: > > MemAvailable+zram[swapfree - swapfree * compress ratio]+swapdev[swapfree] > > Why is this needed to be exported by userspace? Who is going to use > this information and why can't they just calculate it from the exported > information already? In embedded devices, it is necessary to assess how much memory is available. If the memory allocation is based on available+swapfree, it may cause oom and affect the normal use of the devices. And it is more accurate and safe to calculate the swap available memory through minimum compression ratio. Although mm_stat interface provides compressed information，but it is not easy to get the minimum compression ratio during swaping out. Kernel provides a common interface, which makes it easier to use and judge the state of system memory > What tool requires this new information and what is it going to be used > for? It can be used in embedded devices to evaluate the memory condition and avoid causing oom; Also If we wants to know more accurate available memory information when zram is used. > And why add a block driver's information to a core proc file? Shouldn't > the information only be in the block driver's sysfs directory only? > > thanks, > > greg k-h I thought it would be better to put it there. In the first patch, MemAvailable returned with swap available memory, and David recommended a separate interface. thanks
