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Running firefox results in tens of thousands memfds in DEL state - is this a bug?

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deeptho
deeptho

When I run firefox, the following commands lsof |grep -i firefox|grep memfd|wc -l lsof |grep -i firefox|grep memfd|grep DEL|wc -l produce values in the 20 000 or even 100 000 range.

For instance, currently with only 1 tab open - the form on which I type this question - I get $lsof |grep -i firefox|grep memfd|wc -l 19317 $lsof |grep -i firefox|grep memfd|grep DEL|wc -l 16362 And these numbers are still on the low side. In normal use (e.g., 10 tabs open), the numbers reach close to 100 000.

Some example lines of lsof: firefox 3883 135330 StreamT~s xxx DEL REG 0,1 27559 /memfd:mozilla-ipc firefox 3883 135325 Indexed~I xxx 156u REG 0,1 67108864 11945 /memfd:pulseaudio (deleted) firefox 3883 135325 Indexed~I xxx 160r REG 0,1 13192 78 /memfd:mozilla-ipc (deleted) firefox 3883 135427 StreamT~s xxx 132r REG 0,1 170 3110 /memfd:mozilla-ipc (deleted)

Although it may be a problem in lsof, this suggests that firefox performs a lot of memmaps that are later deleted, but are deleted in a way that leaves some left over state. Note that the "DEL" state in column 6 does not always agree with "(deleted)" in the right most column.

I first discovered this issue when my computer started failing with messages like pipewire-pulse[103898]: pw.mem: 0x55ce0273ac50: Failed to create memfd: Too many open files This could be a coincidence of course.

Current firefox version: 137.0 (but also occurs in other versiosn, e.g. 133.0.3) uname -r: 6.12.7-100.fc40.x86_64 OS: fedora 40

When I run firefox, the following commands lsof |grep -i firefox|grep memfd|wc -l lsof |grep -i firefox|grep memfd|grep DEL|wc -l produce values in the 20 000 or even 100 000 range. For instance, currently with only 1 tab open - the form on which I type this question - I get $lsof |grep -i firefox|grep memfd|wc -l 19317 $lsof |grep -i firefox|grep memfd|grep DEL|wc -l 16362 And these numbers are still on the low side. In normal use (e.g., 10 tabs open), the numbers reach close to 100 000. Some example lines of lsof: firefox 3883 135330 StreamT~s xxx DEL REG 0,1 27559 /memfd:mozilla-ipc firefox 3883 135325 Indexed~I xxx 156u REG 0,1 67108864 11945 /memfd:pulseaudio (deleted) firefox 3883 135325 Indexed~I xxx 160r REG 0,1 13192 78 /memfd:mozilla-ipc (deleted) firefox 3883 135427 StreamT~s xxx 132r REG 0,1 170 3110 /memfd:mozilla-ipc (deleted) Although it may be a problem in lsof, this suggests that firefox performs a lot of memmaps that are later deleted, but are deleted in a way that leaves some left over state. Note that the "DEL" state in column 6 does not always agree with "(deleted)" in the right most column. I first discovered this issue when my computer started failing with messages like pipewire-pulse[103898]: pw.mem: 0x55ce0273ac50: Failed to create memfd: Too many open files This could be a coincidence of course. Current firefox version: 137.0 (but also occurs in other versiosn, e.g. 133.0.3) uname -r: 6.12.7-100.fc40.x86_64 OS: fedora 40